Tuesday’s debate will include Sens. Bernie Sanders (I-Vt.), Elizabeth Warren (D-Mass.) and Amy Klobuchar (D-Minn.).

Kaine said he also needs to factor in the structure of the impeachment trial. House Speaker Nancy Pelosi said she will send the articles of impeachment to the Senate this week, which could jump-start the trial as early as Wednesday. Whether the Senate will take up legislative matters during the trial remains uncertain.

“The whole question is ... During impeachment, what else happens?” Kaine said. “It’s often the case that the Dems and [Republicans] will reach an agreement. ... We’ll legislate in the morning, we’ll do impeachment in the afternoon — but can’t take it for granted. We still have to work that through.”

Kaine predicts the vote will happen “in days or weeks” and doesn’t see the absence of the three presidential candidates as an inconvenience.

“I get it,” he said. “If I thought they weren’t going to be here for two months, I’d be frustrated. But they’re going to be here.”

Kaine’s resolution comes as tensions between the United States and Iran have escalated after the U.S. killing of a top Iranian general, Qassem Soleimani, and a retaliatory Iranian strike on bases that house U.S. troops in Iraq. The measure can pass with a simple majority, meaning Democrats will need four Republicans to join them.

Senate Minority Leader Chuck Schumer said Monday the resolution is “needed now more than ever” and suggested the Senate will consider it this week.

Kaine’s resolution gained momentum last week when Republican Sens. Mike Lee of Utah and Rand Paul of Kentucky said they’d sign on. Their comments came after a briefing on the Soleimani strike from top administration officials.

Lee described the briefing as “the worst” he’d seen on a military issue in his nine years in the Senate and lambasted the officials for failing to indicate when they would seek congressional approval for military action.

The uncertain timeline for the resolution also gives Democrats more time to garner additional GOP support. Among the Republicans they hope will join them are Sens. Susan Collins of Maine and Todd Young of Indiana. Collins, who has met with Kaine about the proposal, has voiced concern about its scope and timing.

"I want to make sure that anything I vote on makes clear that the president maintains his Article 2 prerogatives and also that it does not contain any — what I would call political content," Young said, referring to the article in the Constitution that defines presidential powers. He added that Kaine has "gone to some lengths to try and do that."

Senate Majority Leader Mitch McConnell predicted Monday that the Senate would take up Kaine’s resolution soon and vowed to “strongly oppose it,” arguing the chamber could better exercise oversight “through hearings, resolutions and more tailored legislation.” The House passed similar legislation last week.

The GOP leader added that senators should “consider what message the Senate should send to Iran and the world at the very moment that America’s actions are changing the calculus in Tehran for the better.”

