AMES, Iowa — The campaign trail and the impeachment trial were on dual tracks Tuesday, showing that no matter how hard the Democrats try, the 2020 election is very much about one thing: President Donald Trump.

The primary campaign rolled on in Iowa, where campaign organizers are preparing for the final push before the state's critical first-in-the-nation caucuses just two weeks away on Feb. 3, but the bigger political story — and a handful of the leading candidates — were pinned down in Washington for the president's impeachment trial in the Senate.

Sens. Elizabeth Warren, D-Mass., Bernie Sanders, I-Vt., and Amy Klobuchar, D-Minn., had to abandon the campaign trail to report for "jury duty" in the trial in Washington, trading the frigid plains of Iowa for the stately, climate-controlled halls of Congress. Sen. Michael Bennet, D-Colo., who is running a long-shot campaign focused mostly on New Hampshire, was also confined to the Senate.

"This is only the third impeachment trial in the history of the United States," Warren told reporters Tuesday at the Capitol. "Some things are more important than politics, and the Constitution of the United States is at stake here."

Sanders had to cancel an event planned for Wednesday evening in Iowa and responded to an unexpected attack from Hillary Clinton, his 2016 rival for the Democratic nomination, by saying he was too busy with the impeachment proceedings to engage.

"My focus today is on a monumental moment in American history: the impeachment trial of Donald Trump," Sanders said.

Meanwhile, in Iowa, former Vice President Joe Biden dodged questions about his son, Hunter, whose work in Ukraine was part of the reason for the alleged pressure campaign that led to Trump's impeachment.

Pete Buttigieg, the former mayor of South Bend, Indiana, was also campaigning in Iowa on Tuesday. He was candid about the edge he could gain from being able to stay on the trail while other top contenders are stuck in Washington.

"Look, realistically, a lot of people are going to make up their minds in the last few days in each of the early states and here in Iowa, too," Buttigieg said at a campaign stop in Mount Pleasant on Tuesday. "So we're going to make the most of every moment that we have on the ground."

Typically, the final weeks before Iowa votes is a time for candidates to virtually camp out in the state, holding dozens of events in their final pushes.

But this is not a typical election.

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It's a fitting beginning of the end of a yearlong Democratic presidential primary that Trump has overshadowed from the start.

The outcome of Iowa's caucuses are as critical and as unpredictable as at any time in recent memory, Democratic insiders say. But while candidates in Iowa rarely talk with voters about the day-to-day crisis in Washington, Iowa has often felt like an afterthought in the national political conversation.

"As all of you know, tonight I'm going back to D.C., and tomorrow I will be in an impeachment trial," Sanders told supporters Monday night in Des Moines. "How long it lasts? Honestly don't know. I am not going to be able to be here as much as I would like. So you guys are going to have to carry the ball."

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None of the candidates wanted this to happen. Not only does it take them off the trail, but it also distracts from the messages they're trying to convey and the issues they're trying to raise.

But none of the senators running for president publicly expressed any doubt about which side of the split screen — Iowa or Washington — was more important.

"This is my constitutional duty," Klobuchar, who had taken a 6 a.m. flight Tuesday to get back to Washington from Iowa, told reporters in the Capitol. "That is the fact."

White House counsel Pat Cipollone, a leader of Trump's impeachment legal team, seemed to relish the detour.

"Some of you are upset because you should be in Iowa right now," he told senators.

In Iowa, some Democrats argue that not being physically present is problematic for the senator-candidates, especially in a state where voters expect to meet the contenders in person and a premium is placed on retail meet-and-greet politics.

"As people have to spend more and more time in Washington and less and less in Iowa, it will make a difference," said Jerry Crawford, a Des Moines-based lawyer who has played key roles in numerous presidential campaigns in the state. "The most valuable resource at this point in the calendar is time."

Indeed, some of those voters still hope to hear from each candidate — in person.

"I think it's terribly unfortunate," Lisa Smith, who works at a hospital in Des Moines, said as she waited for Warren to speak at a nearby middle school on Saturday. "I just started tuning in because it's hard for me to see everything with my work schedule."

Smith was deciding among Warren, Biden and Sanders, who are bunched at the top of the Iowa polls, along with Buttigieg.

"It will be less exposure for people like me who are undecided, because these are the times where you really start looking into it and figuring out if they align with your beliefs," Smith added. "But I came out today because I knew she might not be back, and I wanted to make sure I could hear from her before making up my mind. If I can, I still would like to meet and see everyone."

Supporters of Sanders and Warren argue that the trial is more damaging to the two other Iowa front-runners — Biden and Buttigieg — even though they will have the state almost entirely to themselves during the trial.

"I think [the trial] will show people the kind of leadership that this type of stuff requires, and maybe they'll think twice about supporting a small-town mayor," Robin Bly, a factory worker from Des Moines who supports Sanders, said in a jab at Buttigieg.

Luann Julstrom, a retiree from Ankeny and a committed Sanders supporter, said Biden's involvement in the impeachment saga and Trump's attacks on him could hurt him.

"You never want 'corruption' and your name in the same sentence," Julstrom said.

A significant number of voters are still up for grabs in Iowa. In a Des Moines Register poll this month, 13 percent of likely Democratic caucus-goers said they did not yet have a favorite, and 45 percent said they could still be persuaded to support another candidate.

Meanwhile, almost all of the senators plan to come back to Iowa this weekend to campaign. But as their campaigns sent around event RSVPs and event schedules, they all came with one caveat:

"Please note: This schedule is subject to change depending on the schedule for impeachment in the U.S. Senate."