Trump in next year's -- or this year's election is about to kick into a new gear.

John Yang reports on the push to win support before the first voters have their say.

JOHN YANG: For Iowa Democrats, decision time is nearing a, campaign buses roll, like this

one with a populist theme carrying Vermont Senator Bernie Sanders

SEN. BERNIE SANDERS (I-VT), Presidential Candidate: How are you doing?

JOHN YANG: Boosted by polls showing his message gaining steam.

SEN. BERNIE SANDERS: Well, we're feeling good. Polls are polls. What matters is the kind

of grassroots activism that we have. We have got people knocking on doors all over the

state.

JOHN YANG: But for the rising candidate, there's rising pressure.

Minnesota Senator Amy Klobuchar told NBC that Sanders is too liberal.

SEN. AMY KLOBUCHAR (D-MN), Presidential Candidate: I don't think he should be leading the ticket.

I think I should be leading the ticket, because my ideas are much more in synch with bold

ways of getting things done.

JOHN YANG: A third senator, Elizabeth Warren of Massachusetts, also zoomed to Iowa during

the weekend break in the impeachment trial.

SEN. ELIZABETH WARREN (D-MA), Presidential Candidate: Good to be in Muscatine.

WOMAN: Hey, Senator.

SEN. ELIZABETH WARREN: Good not to be in Washington.

JOHN YANG: Hers was a topsy-turvy weekend, lagging in some polls, but also scoring the

endorsement from The Des Moines Register editorial board. She, too, made the case that she could

win in November.

SEN. ELIZABETH WARREN: Can we just address it right here? Women win.

(CHEERING AND APPLAUSE)

SEN. ELIZABETH WARREN: We took back the House and we took back statehouses around the nation

because of women candidates and the women who do the hard work to get it done.

(CHEERING AND APPLAUSE)

JOHN YANG: Former Mayor Pete Buttigieg staked his claim to electability on his outreach

to non-Democrats. His venue? A town hall hosted by FOX News.

PETE BUTTIGIEG (D), Presidential Candidate: I'm meeting a lot of what I like to call future

former Republicans who are coming to my events. If you're having trouble looking your kids

in the eye and explaining this presidency to them, then you have a choice.

JOHN YANG: Still, even though Iowa's caucuses are just a week away, it wasn't the sole focus

of the leading candidates.

Former Vice President Joe Biden was in New Hampshire, where the primary is set for the

following week.

For the "PBS NewsHour," I'm John Yang.