Among all voters, Garin argued, “a majority has come to the conclusion that Trump is unfit for the job and that he would represent a significant risk as president.” Polling and focus group testing, Garin said, have shown that one ad produced by Priorities, “Grace,” has been highly effective. It shows Grace, who was born with spina bifida, her parents, Chris and Lauren Glaros, and a clip of Trump ridiculing a disabled New York Times reporter.

The ad concludes with the father on camera:

When I saw Donald Trump mock someone with a disability, it showed me his soul. It showed me his heart. And I didn’t like what I saw.

I asked Garin, along with other strategists and political observers, how they would respond to a long list of Trump’s rambling, theatrical promises, which he would, in fact, be unable to keep. Just a partial list of these includes refusing to defend America’s NATO allies, returning 11 million undocumented immigrants to their home countries, saving $300 billion annually on a prescription drug program that spends only $78 billion a year, nationalizing concealed weapons permits and vowing that “If I become president, we’re gonna be saying Merry Christmas at every store ... You can leave Happy Holidays at the corner.”

Should Democrats, I inquired, point to the infeasibility of Trump’s proposals and the damaging results of any attempts on his part to follow through? That approach would not work, Garin said, because voters, including many of Trump’s supporters, don’t really “believe he will build a wall, or get Mexico to pay for a wall” — they have already discounted many of Trump’s over-the-top assertions as hyperbole.

“The real case has more to do with his character and temperament,” Garin said. “The biggest concern is that he is temperamentally unsuited to lead the country.”

Celinda Lake, a Democratic pollster unaffiliated with the Clinton campaign, argued in an email that there were risks in attacking specific Trump proposals as unrealistic:

To argue you can’t do it just makes you part of the status quo and the problem in Washington. Voters will feel if you say you can’t do some of these things or something in these arenas, we will hire someone who can.

In an interesting warning to Democrats, Arthur Lupia, a professor of political science at the University of Michigan, wrote me:

Responding directly to Trump’s claims often requires repeating them, which gives them extra oxygen. There is a growing literature on attempts to correct “misinformation.” A common theme in this literature is that if a person repeats misinformation or otherwise draws attention to it in an attempt to counter the misinformation, the original claim can be reinforced, rather than diminished, in people’s memories.

Making a related argument, a Democratic strategist who sought anonymity in order to protect his relationship with the Clinton campaign, wrote me:

The problem for Democrats is that in quarreling with the Trump program, they are getting tangled up with specifics, and as a result, they may be seen to be oblivious or insensitive to the underlying message: about illegal immigration or crime or terrorism or loss of local control or American responsibility for world affairs that seems endless and pursued at the expense of concentration on domestic concerns.

This strategist cited the futility of accusing Trump of hyping crime:

This seems counterproductive: Voters are not judging a 10-year performance on crime if they are worried about an experienced or feared increase now. The effect of a defense of this nature may be perceived as belittling or minimizing the concern.

Democrats have to negotiate a tricky path in communicating their candidate’s “identification with the main concerns of many of Trump’s voters” on such issues as immigration, the strategist argued. This empathy has to be

thematic and not programmatic identification: we plainly cannot agree with regressive changes in the tax code, or canceling the Paris agreement, or deporting 11 million people.

Robert Borosage, co-director of the Campaign for America’s Future, a liberal advocacy group, described the problem of attempting to refute Trump point-by-point:

Democratic think tanks and surrogates and experts will dissect his proposals and show how they fail, but that won’t mean much. He’s an attitude, a direction, not a policy agenda.

Clinton’s task, in Borosage’s view, is not an easy one for a politician who has been in the national spotlight for more than a quarter of a century: “H.R.C.’s challenge is to claim the future — one that is different than the past,” Borosage wrote.