By Jon Keller

BOSTON (CBS) – You may think you know how the top Democratic presidential candidates are branding themselves. Then you see the choices they’ve made for their final pitches to Iowa voters.

JOE BIDEN

Joe Biden. (Photo by STEPHEN MATUREN/AFP via Getty Images)

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“Imagine all the progress we can make in the next four years,” says Biden at the start of his closing TV ad. But there’s a more immediate bit of “progress” Biden has in mind.

The perception of electability has sustained his campaign through some bumpy times, and in this ad, he nods to the issues but returns to his core argument: “What we imagine today you can make reality, but first, we need to beat Donald Trump, then there will be no limit to what we can do.” (That may also be a subtle signal to his Democratic doubters that his moderate campaign persona might become more sharp-edged after the inauguration.)

AMY KLOBUCHAR

Amy Klobuchar. (Photo by Sean Rayford/Getty Images)

“We have a president who thinks everything is about him, his tweets, his golf courses, his ego,” says Klobuchar in her TV ad, with that odd juxtaposition of a broad smile while uttering something distasteful. “But I think the job is about you.”

Fine, but curiously, Klobuchar, relentless player of the electability card during debates, doesn’t use it here at all. Perhaps she believes Trump-loathing has run its course in Iowa.

ELIZABETH WARREN

Elizabeth Warren. (Photo by Scott Olson/Getty Images)

But Warren does not think so, making Trump the centerpiece of her latest stretch-run Iowa ad. “I’m going to beat him,” she says confidently, countering lagging poll numbers by arguing she’s Trump’s worst nightmare. “He fears Elizabeth Warren most,” intones a voiceover. “The Trump campaign is internally somewhat concerned about her. They see her as a threat.”

PETE BUTTIGIEG

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Pete Buttigieg. (Photo by Spencer Platt/Getty Images)

But Buttigieg doesn’t mention the president at all, instead leaning heavily on a call for generational change. “It’s time to turn the page from a Washington experience paralyzed by the same old thinking,” he says, as images of admiring young and – in a nod to his poor showing among voters of color – black attendees at his rallies flash on-screen. The Obama 2008 retro vibe continues with Buttigieg, and why not? Look how far it’s taken him.

BERNIE SANDERS

Vermont Sen. Bernie Sanders speaks in Cambridge (WBZ-TV)

In Bernie’s closer, it’s no issues, no Trump, just a purely inspirational approach. “Take a look around you and find someone you don’t know. Maybe somebody who doesn’t look like you. Are you willing to fight for that person as much as you’re willing to fight for yourself?” he asks.

Biden, Buttigieg and Sanders are all sticking with their core messages. That can be a sign of confidence or an admission that it’s too late to shift gears.

Warren’s approach takes on doubts about her own electability while implicitly raising them about Sanders; this may be a recognition that her effort to pry the left away from Bernie has stalled.

And Klobuchar can’t seem to decide if she’s Minnesota nice or ready to pin Trump to the mat.

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We’ll find out Monday night who had the right idea.

Jon Keller