Washington (CNN) As the clock above the entrance to the Senate chamber inched toward 9:30 p.m. ET on Wednesday night, Minnesota Sen. Amy Klobuchar looked antsy.

It was nearly time for her "tele-town hall" virtual meeting with potential Iowa caucus-goers, and while the impeachment trial of President Donald Trump appeared to be winding down for the night, it was clear she was going to be late.

As Senate Majority Leader Mitch McConnell officially closed the session, Klobuchar was already halfway to the door, a purse over her shoulder, before any of the other senators had risen from their desks. After a quick ride across Constitution Avenue to an office building just off Capitol Hill, she finally joined the town hall just after 10 p.m. -- video conferencing in from a drab conference room.

Klobuchar began with an apology: "Sorry, this is a little later than we planned."

In the crucial days before the first nominating contests of the Democratic presidential primary (Iowa on Feb. 3, New Hampshire on Feb. 11), something strange has happened. Amidst a highly competitive race, four of the remaining candidates have been forced off the trail to go back to Washington for the impeachment trial.

While senators who run for President periodically have to return to Washington for a vote or a hearing, an impeachment trial is altogether out of the norm, and has meant that along with Klobuchar, Sens. Bernie Sanders, Elizabeth Warren, and Michael Bennet, have all had to disengage from their campaigns.

Not only are they stuck in Washington, they have to spend long hours out of contact each day. Senate rules force them to relinquish their phones while they listen to fellow Democrats make the case to impeach the man they'd like to defeat as President in ten months.

Meanwhile, two of their leading rivals, former Vice President Joe Biden and former South Bend, Indiana, mayor Pete Buttigieg, are pressing their advantage during the final stretch before voting begins.

Sen. Elizabeth Warren, talks to the media as she walks to the Senate chamber prior to the start of the impeachment trial.

It's unclear how this dynamic will affect the election, and whether the senators will pay a political price for their absence. It will certainly test the quality of the groundwork many of them have done in the early states over the past year.

"I know what's going on right now back in Iowa," Warren told CNN's Dana Bash on Thursday. "And that is that this grassroots movement that I've spent over a year building is active."

For Sanders at least, who's seen a recent rise in early-state polls , it also means he can't capitalize in person on the momentum.

"I'm going to be stuck in Washington for God knows how long," Sanders jokingly told a crowd of supporters in Des Moines, Iowa, on Monday. "So we need you to take my place, give 2-hour speeches like I do."

Compared to some Republicans and a few of their Democratic colleagues, the four White House hopefuls have been more attentive and focused on the lengthy, hours-long presentations during the trial. It's also given them a chance to socialize with each other in a way they may not as competitors on the trail or at a debate.

Late on Wednesday, as the House managers continued their opening arguments, Sanders and Klobuchar chatted and smiled with each other as they paced around the chamber.

Warren, on the other hand, has been less social and more attentive, staying at her desk along the front wall of the chamber and dutifully taking notes. A week after a contentious public disagreement with Sanders over their recollection of a private conversation, the two progressive senators have not been seen talking together during the trial.

The proceedings haven't completely sidelined the Senate-based candidates. Technology enables virtual campaigning, such as Klobuchar's town hall and Bennet's appearances on Facebook Live. During breaks or trips to the cloakroom, the candidates can call up their campaigns to stay up to date.

"I certainly am staying in touch with them. We're having conversations in the morning and evening," Bennet told CNN Thursday.

But that's not the same as being there in person, especially when it comes to Iowa and New Hampshire, where the contests are often marked by last minute retail politicking through the cold and snow. The campaigns have had to lean heavily on surrogates instead.

In Iowa on Wednesday, Klobuchar's 24-year-old daughter, Abigail Bessler, appeared at her first campaign event of her mother's presidential bid. Klobuchar made sure to mention her daughter to reporters during one break, noting that Bessler had texted her to say she was in good company by campaigning "up against AOC" -- that is, Rep. Alexandria Ocasio-Cortez, one of Sanders' surrogates in Iowa this week.

The singular focus on the trial by much of the news media means there's no shortage of cameras and reporters for candidates to directly amplify their messages. Just minutes before the trial began on Thursday, Warren made the most of a question from a reporter to mention her campaign website.

"People across Iowa, across the country, have gone to ElizabethWarren.com," she said, when asked about how she is dealing with her opponents drawing large crowds in the Hawkeye State as the trial went on in DC. "They said I want to help in any way I can, make phone calls, pitch in five bucks, knock on doors."

And Klobuchar used a national TV interview to reinforce an Iowa-tailored message.

"We have the most endorsements of Iowa legislators and farmers and anyone in the race and to me that means they're in the room, they're at the grocery stores, they are completely committed to helping me," Klobuchar said during an appearance with CNN's Dana Bash during an afternoon break from the trial.

Each campaign is heading back to an early state during the weekend. Sanders has a rally in Iowa with Ocasio-Cortez on Saturday night, and will continue to campaign there Sunday. Warren and Klobuchar will also travel to Iowa this weekend, while Bennet is going to New Hampshire.

But even a quick weekend campaign jaunt could be grueling, since all four will need to back to Washington in time for the next trial session on Monday afternoon.

And then there's the issue of raising money. A spokeswoman for Bennet's campaign said the Colorado Democrat "will not conduct any campaign fundraising while the trial is in session.

Sanders, the field's strongest small-dollar fundraiser, had a different approach.

"With impeachment under way in the Senate, Bernie isn't going to be able to spend as much time as he would like in Iowa and New Hampshire," read the body of a fundraising email on Thursday. "We share that not to complain -- Bernie is going to fulfill his solemn constitutional obligation. But he does need us to pick him up."

The email's subject line was a single word, echoing his remarks earlier in the week: "Stuck."