DES MOINES, Iowa — Freed momentarily from the Senate’s impeachment trial, several presidential candidates high-tailed it to Iowa on Saturday for a last-minute blitz of campaigning before the state’s caucuses kick off the battle for the Democratic nomination.

Sens. Elizabeth Warren of Massachusetts, Bernie Sanders of Vermont and Amy Klobuchar of Minnesota planned to hold town halls, rallies and concerts across Iowa on Saturday to keep their supporters motivated heading into the final stretch of the caucus campaign. They’ll join former Vice President Joe Biden and Pete Buttigieg, the former mayor of South Bend, Indiana, who don’t have Senate obligations and have already spent much of the past week in Iowa.

The burst of campaigning comes as the contest for the Democratic nomination enters a critical – and volatile – phase. A New York Times/Siena College poll released Saturday showed Sanders with a slight edge over the other leading candidates, but the race remains competitive. Several polls show Biden, Buttigieg and Warren are still among the front-runners.

Democratic presidential candidate former South Bend, Ind., Mayor Pete Buttigieg, speaks during a town hall meeting at the University of Dubuque in Dubuque, Iowa, on Wednesday. Gene J. Puskar/Associated Press

“There’s still plenty of time for movement,” said Kurt Meyer, chairman of the Tri-County Democrats in northern Iowa. “Every part of the ground game counts.”

Stuck in Washington for much of the past week, the senators in the race have flooded Iowa and other early voting states with top-shelf surrogates – rock star lawmakers, former Cabinet members, celebrities and spouses. The stand-ins aren’t a guaranteed way to sustain excitement or win votes, but the campaigns see it as the best way to maximize their reach in a nominating fight that could turn on the narrowest of margins in Iowa and other early states.

Biden isn’t bound to the Senate like some of his rivals, but he must navigate the trial nonetheless. House Democrats’ charges that Trump abused his power and obstructed Congress are rooted in the president pressuring Ukrainian officials to investigate discredited theories about Biden’s foreign policy duties in Ukraine as vice president and his son Hunter’s personal business dealings there.

After a brief trip to New Hampshire, the second state to vote in Democrats’ nominating process, Biden planned to return to Iowa on Saturday evening and intended to remain in the state until caucus day. He began the day announcing an endorsement from U.S. Rep. Cindy Axne, who joined her fellow first-term congresswoman from Iowa, Abby Finkenauer, in backing Biden.

Ahead of his arrival in Iowa, Sanders sent progressive icon and New York Rep. Alexandria Ocasio-Cortez to the state. She addressed dozens of Sanders volunteers at one of his field offices inside a strip mall, before heading out to canvass in Cedar Rapids. She promised to wear her green “Green New Deal” baseball cap to join them on a clear but cold Saturday, amid snow drifts that piled along plowed roads, and melting ice.

“We are here to make a revolution that lasts,” Ocasio-Cortez said.

She will later join Sanders and filmmaker Michael Moore for a Saturday night rally in Ames.

Sanders’ wife, Jane, and actor Danny Glover were campaigning on his behalf in Nevada, which hosts the third nominating contest. Jane Sanders predicted a strong showing in the early voting states.

“I think we’ll win Iowa,” she told about 40 staff and volunteers. “I think we’ll win New Hampshire. And then I think it’s up to you whether we win Nevada. But it looks great.”

Sanders’ apparent momentum in Iowa is enough for the Buttigieg campaign to respond. The campaign sent prospective donors a fundraising solicitation warning of the Vermont senator’s strength.

“Bernie Sanders is raising tons of money, he’s surging in the polls, and he has dark money groups attacking his competitors,” the email said. “If things stay steady until the Iowa Caucuses in just nine days, Bernie Sanders could be the nominee of our party.”

Warren has Julian Castro, the former Obama housing secretary and onetime presidential candidate, in Nevada. U.S. Rep. Ayanna Pressley, D-Mass., another star of the House freshman class like Ocasio-Cortez, is in South Carolina.

The Senate adjourned about noon on Saturday, giving the presidential candidates time to return to Iowa for late-afternoon and evening events. Sen. Michael Bennet, D-Colo., was going to New Hampshire.

The weekend is critical for them, depending on how many more days the trial will extend this coming week. Warren’s campaign on Saturday hit prospective donors with a frank plea ahead of an “important January fundraising deadline.”

Fall short of her financial targets, the campaign wrote, and “we risk having to scale back our advertising plan during the most critical period of this election.”