Before I continue, I want to bullet-point the critical facts you need to take away with you:
- Extreme reactionary Antonin Scalia was elevated to the Supreme Court by a Senate vote of 98-0. Those weren't 98 Republicans. Scalia was later one of five GOP apparatchiks on the high court who stole the 2000 presidential election for George Bush (Bush the Younger). 
- Democratic Senator Joe Biden (later vice president in the regime of Barack "The Drone Assassin" Obama) functioning as chairman of the Senate Judiciary Committee, was instrumental in putting known sex offender Clarence Thomas on the Supreme Court. Thomas, like Scalia, voted to steal the 2000 presidential election for the GOP (Gang Of Plunderers). 
- EVERY reactionary elevated to the top court, with its immense power, has gotten there with the support of Democratic Party senators. Even the ones who vote against confirming them soft-pedal how awful and evil the nominees are.
- In the last year of the presidency of Hit Man Obama, a vacancy opened up on the Supereme Court. In an unprecedented power grab, the Senate Majority Leader, Republican Mitch McConnell (a venal coal industry stooge from Kentucky) announced that Obama would not be allowed to fill that vacancy. And Democratic response was- some grumbling under their breath and acceptance. Obama himself didn't give any evidence of even caring! (Yet there are still morons who think he is a "progressive" who was somehow thwarted by forces beyond his control. Now imagine if the situation was reversed, and a Democratic-controlled Senate denied a GOP president the right to fill a Supreme Court vacancy! There would be DAILY howls of outrage, even calls for a military coup "to restore the Constitutional order." That's because the Republicans are like rabid wolverines and are serious about power. That's how, with a minority of the populace behind them, they have taken over the presidency, the Congress, the Judiciary, and two-thirds of the state legislatures and governorships. (They have long dominated and controlled the military and secret police apparatus.) They have used their control of state legislatures to draw districts that allow them to elect the majority of Representatives to the national House of Representatives with a minority of overall voters. The Democrats are mainly a party of grifters, unserious about power, just looking for profitable sinecures for themselves.
Okay, that last bulletpoint was a long one, but essential. Now on to the body of the essay, which will illustrate the utter cynicism of the Democrats in manipulating people who are duped into relying on them to protect the few hard-won rights we have.
Every election "cycle," which is to say, every two years , Democratic political hacks running for office send out tons of political junk mail to citizens, hoping to woo their votes. One of the perennial themes of this propaganda bombardment is how the Supreme Court hangs in the balance, and the need to protect the right to abortion, which was only granted to women by a divided Supreme Court in the Roe vs. Wade decision. That decision was made under pressure from the women's movement, and only granted a limited right, in the first trimester of pregnancy, after which the government was deemed to have an "interest" in interfering in personal and medical decisions and exerting control over people's bodies.
In the years since, the organized reactionaries of the U.S., including the Republican Party (GOP), rightwing religious zealots, the Catholic Church bosses, and assorted rightwing media and political cadres, have relentlessly attacked abortion. The terrorist arm of this novement has assassinated doctors and clinic workers with bombs and guns, committed thousands of arson and other attacks on abortion clinics, blockaded clinics and much else. The legal offensive has been even more devastating, with states controlled by the GOP (Gang Of Plunderers) virtually eliminating abortion clinics by various legislative encumbrances that in effect persecute the clinics. Some states have functionally outlawed abortion drugs, which in early pregnancy are the cheapest and easiest way to terminate a pregnancy. (By the way, these same creeps who care so much about "unborn children" are the same ones who deport children fleeing gang and state violence south of the U.S. border back to their deaths, who destroy water containers left in the desert for them, who rip children and infants away from their refugee parents and separate them by thousands of miles. They have historically supported the murder of children by fascist death squads in the U.S. empire, and bombing cities and villages in Vietnam, Korea, and elsewhere that kill large numbers of children, babies, and mothers. So I have a sneaking suspicion that reverence for the sanctity of life isn't their actual motive.)
There IS no abortion provider in almost every town in the U.S. Over 90% of U.S. counties have no abortion facility. Abortion has been stigmatized and isolated, banished from the body of the medical profession. The cowardly medical schools don't even teach their students how to perform abortions,
And what has the Democratic Party been doing all the while the assault on abortion rights has continued unabated for 44 years?
Every election they yell at their voters that the right to abortion is under assault and therefore you must vote for them. And that's pretty much it.
And they ensure that the Supreme Court has a hard rightwing majority, They do this to have a scare tactic to run in elections on, and they do this because they too are fundamentally reactionaries. They serve the corporate oligarchy, which of course wants a reactionary judiciary. They believe in state power over citizens- as the repressive legislation pushed into law by their presidents Truman, Clinton, and Obama proves. Obama gave the government the power to indefinitely imprison U.S. citizens in military gulags without charges or legal representation, by government fiat. The government need only label the victims "terrorists." That is now law because of Obama.
Let's dispose of another myth. The repeated, false assertion that the court is divided into a "liberal" wing and a "conservative" one. The actual division is conservative and reactionary. The conservatives ("liberal") mostly try to preserve the status quo, which is the definition of conservatism. The reactionaries want to change the status quo to make it more repressive, and to decrease the influence of the population and give the rich and large corporations ever more power. This is a program of radical change, NOT "conservatism."
1] In a bit of ironically poetic justice, the Democratic candidate who along with his party let the GOP steal the 2000 election, Albert Gore, was one of the Senators who voted to put Scalia on the Supreme Court.
2] Biden made sure Thomas, an arch-reactionary black man who is an enemy of African-Americans in many ways, including his attacks on affirmative action, made it through the confirmation process by stifling witnesses who would have buttressed Anita Hill's testimony about Thomas' vulgar sexual harassment of his underlings, and more critically Biden privately assured his Democratic Senate colleagues not to believe Hill. The story of Biden's treachery is told in the book "Strange Justice: The Selling of Clarence Thomas," by Jane Mayer and Jill Abramson. The authors were reporters at the Wall Street Journal at the time the book was written. Mayer went on to be a staff writer at The New Yorker magazine, where she is today. Abramson became the very first female to ascend to the top editor post at the oh-so-august New York Times.
Abramson's tenure as top editor was short. She accidentally discovered that the publisher and chairman, Arthur Sulzberger Jr., whose family has long owned the paper and its other properties and who inherited his job from his Daddy, was chiseling her on her pay, paying her less than her male predecessors. Sulzberger was miffed when Abramson confronted him about this, proceeded to fire her, and then engaged in a campaign of character assassination against her.
So "liberal" of him!
This sexist asshole also hired the scandalous former BBC boss Mark Thompson. After notorious pedophile and BBC star Jimmy Savile died, the BBC had an expose ready to air. That was killed, and in its place a tribute to Savile was aired. Thompson claimed to know nothing about any of this, despite being in charge. Sulzberger thinks this guy is worth paying millions for.
The result so far has been a discrimination suit against Thompson for the toxic environment he's helped create (or perpetuate) at the NY Times. Two black female employees allege in their lawsuit that Thompson introduced an "environment rife with discrimination based on age, race and gender." It further links his behavior to similar actions by him during his BBC tenure. ["New York Times chief executive accused of discrimination," BBC News, 29 April, 2016.]
3] In the U.S., one chamber of the national legislature, the "House of Representatives" of the U.S. Congress, stands for election every two years. There are 435 Congressional districts, thus 435 representatives covering all the 50 states. Congressional districts are proportioned roughly by population.
The other chamber of Congress, the U.S. Senate, has 100 Senators, two Senator for each state. This gives grossly disproportional weight and power to sparsely populated states hard rightwing states, and greatly weakens the political weight of populous states. So California has two Senators, and the 20 least populous states, whose total population equals that of California, have 40 Senators. So arch-reactionary states like Wyoming, Montana, Idaho, the two Dakotas, Iowa, Arkansas, Louisiana, and so on, are a powerful structural and institutional factor in making the U.S. a rightwing nation, even though only a minority of the population is rightwing in this putative "democracy."
Senators are elected for six year terms. Every two years, one third of the Senate stands for reelection.
U.S. presidents serve 4 year terms. The years that aren't presidential election years are called "off-year elections."
The terms of Congresspeople and presidents is set out in the Constitution. The Republicans passed a Constitutional amendment in the 1950's limiting the president to two elected terms. This was done in reaction to the fact that the Democrat Franklin Delano Roosevelt was elected president four times in a row starting in 1932. Ironically, Republican Dwight David Eisenhower, elected in 1952 and 1956, may well have won a third term if not for this amendment.