(CNN) First things first: The theme song of the week is the theme from The NBA on CBS .

A new Kaiser Family Foundation poll finds 55% of Democrats and Democratic leaning independents say they want to build on the Affordable Care Act when asked which approach to health care they prefer. That's far larger than the 39% who say they want to replace the ACA with a national "Medicare for all" plan.

This matches polling from earlier this year which demonstrated a majority of Democrats would prefer to take a more incremental approach to health care.

Perhaps the biggest news coming out of this week's CNN presidential debates was the seeming criticism of former President Barack Obama's policies while in office. It was a stunning turn because anyone looking at the polling data can see that Obama and many of his policies (such as the ACA) remain popular. Democratic candidates who go after Obama too hard risk losing support in the primary and the general election.

Beyond the poll numbers above on the ACA, take a look at Obama's favorable rating since he left office. Among potential Democratic primary voters, a 2017 Pew Research Center poll found that Obama's approval rating stood at 95%. A 2018 CNN poll put his favorable rating among self-identified Democrats at 97%. A May 2019 CBS News/YouGov poll showed that a grand total of 2% of Democrats rated Obama's presidency as "poor." A near unanimous 91% told CBS News/YouGov that it was good or excellent.

When pitted against other past presidents since World War II, Obama's clearly the most popular among potential Democratic primary voters. A Quinnipiac poll taken last year found that 44% said Obama was the best. The second closest, Bill Clinton, came in far in back at just 14%.

All of these numbers are even starker among black Democrats. Obama's favorable rating among them stood at 99% in a 2017 Pew poll His unfavorable rating was 0%. A clear majority of 57% said he was the best president since World War II in the Quinnipiac poll.

Obama's ongoing popularity among black Democrats partially helps explain why former Vice President Joe Biden's has such strong support from them. Biden has cited Obama's name so often you might think Obama was running with him again. It seems to be paying off for Biden -- a recent Quinnipiac University poll has him winning 53% of the black vote in the primary.

You can see how being attached to Obama directly helps Biden through a question asked by Monmouth University in May. Biden took 44% of the primary vote among those who said it was very important for the Democratic nominee to build on Obama's legacy. No other candidate had greater than 15% support. Biden's vote share fell to 25% among those who said it wasn't very important build on Obama's legacy.

Democrats who critique Obama could be doing harm to themselves among the general electorate as well. Obama remains one of the few Democrats popular among voters the party's nominee likely needs to win in order to take back the White House. In a national CNN poll last year, 55% of voters said they thought Obama was a better president than Donald Trump. That was far above the 39% who said Trump was better than Obama.

Of course, elections in this country are won on the state level -- and Obama is popular in the important states. In the 2017 Pew poll, 57% of voters said they had a favorable view of Obama in a combined sample of Michigan, Pennsylvania and Wisconsin, all of which he won in 2008 and 2012. These were the three closest states that Trump won in 2016 and would have put Hillary Clinton over the top in the Electoral College, had she taken them.

When candidates go after Obama from the left, it could be seen as especially dangerous electorally speaking. Trump is already trying to make the Democrats be seen as too far from the center. Going after one of the few popular Democrats for not being far enough left helps make Trump's case for him.