In the context of healthcare in the United States, a pre-existing condition is a medical condition that started before a person's health benefits went into effect. That describes about 50% of medical insurance claims.
Socialism. That's what some people think of when they hear the term "Obamacare" or more formally, the Affordable Care Act (ACA). Ask them how to spell "Socialism" or define it and most can't. What they really mean (history lesson time) is that somebody in the White House remembered how Sen. Joe McCarthy (November 14, 1908 – May 2, 1957) was an American politician who served as a Republican U.S. Senator) and made a name for himself by leading the Republican-led House Un-American Activities Committee (known as HUAC) to expose communist (socialist, marxist) subversion in the USA. Nearly worked, too, until he went too far in accusing everyone, at which point he was asked "have you no shame, Sir?" That's what's behind the whole name-calling "socialist, marxist, left-wing" business. Its meant to distract the average Voter with a little "don't look over there; look over here and see what I want you to see. Stage magicians do it all ther time. 10 points to you if did not fall for that one.
SO, if you educate yourself a bit and you'll find that the BIG battle over this and why the Trump Administration is working overtime to get rid of this is simple: it currently covers pre-existing conditions. That's why President Trump is plowing full speed ahead in getting another Supreme Court Justice appointed, because the Supreme Court is hearing this court case right after the election date in November.
Paying medical insurance claims related to pre-existing conditions costs medical insurance companies millions, maybe billions every year. That's why the major medical insurance companies gave million of dollars to Republican Senators, Congressional Representatives, and the President Trump's re-election campaigns to get rid of it.
We NEED the ACA. President Trump keeps telling everyone that his replacement health care plan is "ready to go" but has still not rolled it out. He says he wants to "get rid of it and replace it, but he has nothing to replace it with. Deduct 10 points now if you have fallen for THAT one.