At 1 p.m. on Tuesday afternoon, every senator participating in the impeachment trial of President Donald Trump will be commanded by the Senate sergeant-at-arms “to keep silent upon pain of imprisonment.”

But for the four senators who also happen to be running to replace Trump as president, silence will feel a little like imprisonment.

With the Iowa caucuses less than two weeks away, the sudden removal of four Democratic presidential hopefuls from the field—including three of the five highest-polling candidates—presents an unprecedented challenge for campaigns desperate to prove their staying power in the early states.

“Closing strong in Iowa is so much about energy and momentum—and so much of that comes from events and the coverage they drive. And there’s no substitute for a principal-level event,” said Patrick Dillon, who worked as a senior battleground states adviser for President Barack Obama’s re-election campaign, and served as chief of staff to former Iowa Governor Chet Culver. “People want to be with a winner, and they see you standing in front of growing, energetic crowds and they see the news you make on the ground in Iowa, and that can be self-reinforcing.”

In a normal field and a normal campaign, voters’ minds would largely be settled by this point, but with razor-thin polling margins between the top four candidates, every handshake at every roadside diner can make a difference.

“In-person is always preferable,” said Prof. Dennis Goldford, a professor of political science at Drake University in Des Moines. “At this point in a long, long caucus season, their absence from the ground is not a huge factor, but in a tight race a feather on the scale can make a difference.”

Each of the senators running for the nomination have publicly declared that they are more than prepared to “chew bubble gum and walk at the same time,” as Sen. Bernie Sanders (I-VT) told reporters on Capitol Hill after being officially sworn in as a juror in Trump’s impeachment trial on Thursday.

“I am a mom—I can do two things at once,” Sen. Amy Klobuchar (D-MN) said on CBS This Morning on Jan 17. “I have a fantastic operation with people who are incredible—in every major town in Iowa. I've got my husband and daughter out this weekend in New Hampshire and then on their way to Iowa. And I'm gonna be there for three days. I am a mom. I can do two things at once.”

But in Iowa, where presidential candidates are expected to do everything short of taking voters out for an ice cream cone in order to win their support, absence from the campaign trail could be a major competitive disadvantage—particularly as former Vice President Joe Biden and former Mayor Pete Buttigieg, both riding high in the polls and with cash to burn, are unencumbered by the senatorial equivalent of jury duty.

“If you’re in a strong position now, it’s slightly less scary I guess—you just try to count on your organization to maintain and hope that committed volunteers and organizers eke out expansion where they can,” said Dillon. “But if your plan was to get hot at the end and close strong, then honestly you really needed that on-the-ground presence just to juice your organization up its highest level anyway—so that’s a big challenge.”

Klobuchar, who has described her position in Iowa as a “strong fifth place,” has bet the farm on a come-from-behind strong finish in the Hawkeye State. Her campaign told The Daily Beast that she is confident in its three-part plan for navigating the impeachment trial: organizing, tele-town halls, and flooding the zone with surrogates.

“We really have the strongest slate of endorsements in Iowa of all the candidates,” a campaign official told The Daily Beast, noting that Klobuchar has racked up the endorsements of 13 current and former state legislators, more than any other presidential candidate. “We plan to host a number of teletownhalls, with a number of surrogates—Amy’s husband and daughter will be there, as well.”

“Technology is an amazing thing—Amy can still do TV hits and phone conferences,” the campaign official said, while on-ground organizers “keep the drumbeat alive.”

Some of that organizing was the result of a fortuitous scheduling delay. On Jan. 11, in anticipation that articles of impeachment would be delivered to the Senate at any moment, Klobuchar’s campaign mounted a “Full Klobuchar Day of Action,” in which 41 surrogates helped lead organizing events in every one of Iowa’s 99 counties. The surrogates, who included state legislators, labor leaders, state Democratic Party activists and Klobuchar’s husband, law professor John Bessler, helped canvass caucus-goers, phone-bank, and held organizing meetings.

But Klobuchar still lags behind several other candidates in her Iowa organization efforts—as of last week, the Minnesota senator’s campaign has 18 offices in the state, and more than 80 staffers. Buttigieg’s and Massachusetts Sen. Elizabeth Warren’s campaigns, for example, both have nearly double the number of offices and staff.

Ben Halle, Buttigieg’s Iowa communications director, told The Daily Beast that the former mayor of South Bend, Indiana, will be campaigning at a marathon pace for the final two-week stretch before the caucuses.

“We’re getting Pete in front of as many Iowans as possible,” Halle said. “While Pete was speaking to hundreds in Sioux City, we had more than 250 precinct leaders in Des Moines learning what to do on caucus night.”

That's ground game, Dillon told The Daily Beast,

“There’s only so much an organization, even a well-planned, well-resourced one can do,” Dillon noted, “and it’s a real impediment to a campaign that hasn’t yet been able to build a big ground game in part because they haven’t started getting momentum until recently.”

Sen. Michael Bennet’s spokesperson told The Daily Beast that the the Colorado senator is holding 50 town halls in New Hampshire in the final weeks before that state’s primary—which, due to scheduling and the shorter distance between the state and Washington, D.C., makes his campaign’s focus on the Granite State a fortuitous strategy.

“Michael’s Senate duties, and his responsibility to uphold the Constitution and rule of law, come before any campaign,” the spokesperson said. “Every chance he gets, he will be on the campaign trail talking to early state voters. He is holding 50 town halls in New Hampshire in the final weeks before the primary, answering every last question, to show why he is the best candidate to take on and beat Donald Trump.”

But while Warren and Sanders, who are both heavily investing in Iowa, both boast a heavy on-ground presence and a stable full of high-profile endorsers, not all of their surrogates know what is expected of them during the impeachment trial.

“I’ve done some surrogate work so far but I haven’t received any specific requests for the next few weeks,” said State Sen. Zach Wahls, a Warren endorser and rising star in the state Democratic Party who has made appearances at campaign events geared towards young voters.

State Sen. Liz Bennett, another Warren endorser, told The Daily Beast that she is scheduled to lead a number of canvasses over the final few weeks before the caucuses, “but I think that falls under normal [get-out-the-caucus] activities.”

Asked about its plans for utilizing surrogates during the impeachment trial, Warren’s team told The Daily Beast that former Housing and Urban Development Julián Castro, as well as other high-profile supporters, will be out in force in the closing weeks before early voting begins and as she serves as a juror in the impeachment trial.

Castro, who unlike prominent Sanders surrogates like Rep. Alexandria Ocasio-Cortez (D-NY) or fellow Warren supporter Rep. Ayanna Pressley (D-MA) is not a current office-holder, is seen as a potentially critical member of Warren’s team of surrogates—able to appear at multiple events a day, and with the message-discipline skills of a former presidential candidate to boot.

As a dyed-in-the-wool progressive who embraced (and occasionally inspired) many of Warren’s signature policy proposals long before his endorsement, Castro is in a unique position to help heal Warren’s rifts with left-wing voters who are potentially leaning toward Sanders, a former aide to the candidate’s defunct campaign told The Daily Beast.

“The wing of the party that Julián and Warren represent… is at its best when it is squaring off against Republicans and centrist Dems,” the aide said. “The unity message is part of that—reminding voters that the fight isn’t between progressives.”

Still, Iowa political experts told The Daily Beast that even the most robust organization and surrogate operations amount to guesswork in the uncharted territory of campaigning during impeachment.

“I have no basis to judge how this will play out,” said J. Ann Selzer, a pollster and president of the highly regarded Des Moines-based polling firm Selzer & Company. “Too many moving parts, and zero historical references. I’m as interested to watch as you!”

—Additional reporting by Jackie Kucinich