For Clinton, who has latched herself to President Obama throughout both the primary and general election, this should be a very bad development. Very bad.
If you wanted to make the case that Clinton represents an extension of the bad part of the Obama presidency, this is a gift of epic proportions. EPIC.
Here's the problem: Donald Trump is the Republican presidential nominee. He has spent the last few weeks dealing with allegations of sexual harassment from 11 women and a hot mic tape in which he made a series of lewd comments about women. That's not to mention his a) attacks on fellow Republicans as insufficiently loyal to him, b) insistence that the entire process is rigged, and c) description of Clinton in the final debate as “such a nasty woman.”
Trump, through those and any number of other self-inflicted wounds, has made the election a referendum on him. The question most voters are asking themselves is, “Do I trust him to be president?” and the answer, judging from polls both nationally and in swing states, is a resounding “no.” Trump, largely via his own aversion to staying on message, has so badly damaged himself as a messenger in the eyes of many people that he can't credibly attack Clinton in the way a more orthodox Republican nominee could.
There may be some rallying to Trump's side among rank-and-file Republicans who have been resistant to getting behind him — as this Obamacare news will serve as a stark reminder of everything they didn't like about the Obama presidency. But, it's hard to see any sort of major groundswell toward Trump in the same way there might have been for a Mitt Romney in 2012 or even, say, a Marco Rubio or Ted Cruz in this election.
The game plan to beat Clinton has never been complicated: Make the race about her. Make her own all of the bad stuff people believe she, her husband, and Barack Obama have done during their respective times in office. Present yourself as a reasonable — and safe — alternative to that. Done and done.
Trump has, of course, made the contest entirely about him. Which significantly lessens his ability to capitalize on the Obamacare news, which should be a massively negative development for Clinton's chances of winning the White House. And that is the story of this election.