How Jill Biden gave away the secret to Joe Biden's 2020 plan

"We know in our bones this election is different," the ad's narrator says at the start of the commercial. "The stakes are higher. The threat more serious. We have to beat Donald Trump. And all the polls agree Joe Biden is the strongest Democrat to do the job."

On that last line, a series of bar graphs pop up on screen, showing a variety of polls where Biden is beating Trump in hypothetical 2020 matchups.

The ad, which started running Tuesday morning, comes on the heels of the most blatant appeal to electability yet from the Biden camp.

"I know that not all of you are committed to my husband, and I respect that," Jill Biden, the former vice president's wife, told a crowd at a campaign event in New Hampshire on Monday. "But I want you to think about your candidate, his or her electability, and who's going to win this race."

Added Jill Biden: "Your candidate might be better on, I don't know, health care, than Joe is, but you've got to look at who's going to win this election. And maybe you have to swallow a little bit and say, 'OK, I personally like so-and-so better,' but your bottom line has to be that we have to beat Trump."

Which is, well, putting it out there!

The decision by the Biden camp to lean in so heavily on the electability issue is a risk -- albeit a calculated one. Traditionally, primary voters vote with their hearts, not their head. That is to say they tend to choose the candidate that inspires them, not the candidate they think can win. Primary voters don't tend to cast strategic votes with an eye toward the general election. They vote for what they want their own party to look like.

There are, of course, exceptions -- most notably the 2016 Democratic presidential primary in which Hillary Clinton beat Bernie Sanders at least in part because Democrats believed she represented a better chance to keep the White House in Democratic hands.

Clinton's loss to now-President Donald Trump would have seemed to set back the electability argument in future races. (The fact that Trump is president is, in and of itself, a pretty strong argument against prioritizing supposed electability when choosing a candidate.)

And yet ... the new CNN-SSRS poll, which shows Biden maintaining a double-digit lead over Sanders and Sen. Elizabeth Warren (Massachusetts), suggests that at least at the moment, the electability argument has real salience for Democratic voters. A majority (54%) said that they prioritize nominating a candidate who can beat Trump in November 2020 while just 39% say the most important thing in picking a candidate is that the nominee agrees with their views on issues. (Worth noting: The electability numbers have fallen slightly in the CNN poll; in late June, 61% said a candidate who could beat Trump was the most important element of their vote.)

It's not terribly complicated to understand why electability matters more to Democratic voters in 2020. It's Donald Trump. That's it. While Democratic base voters are rarely thrilled with the actions of a Republican president, Trump's willful disregard of even a semblance of presidential norms coupled with his appointment of two Supreme Court justices, his rolling back of a slew of environmental regulations, his provocations on race and his bullying have made Democrats absolutely desperate to beat him in 2020.

If ever electability was going to be the deciding factor in choosing a Democratic nominee, it's this moment.

The one obvious problem for Biden is that if voters come to believe that while he is the best person to beat Trump, he's not the only person who can do it. Take the latest Fox News poll. Yes, it showed Biden ahead of Trump by 12 points -- 50% to 38%. But it also showed Biden's main rivals for the nomination -- Sanders, Warren and California Sen. Kamala Harris -- also all leading Trump by between 6 and 9 points.

If more results like that one come out, the question voters will have to ask themselves is whether a 12-point lead over Trump is so much larger than, say, a 7-point lead that they have to -- to borrow Jill Biden's words -- "swallow a little bit and say, 'OK, I personally like so and so better,' but your bottom line has to be that we have to beat Trump."

How Democratic voters decide that question remains to be seen. But there is now no question that Joe Biden is running on electability, electability, electability.