The Senate is barreling toward a procedural vote Wednesday on the fiscal 2020 defense authorization bill, but the typically bipartisan measure could become the victim of a filibuster amid a battle over amendments.

Democrats could block cloture on the bill if they don’t receive assurances from Senate Republicans of a vote on an amendment that would stop President Donald Trump from launching a war against Iran without congressional approval.

On Tuesday in the Oval Office, Trump said he had no exit strategy in the event the United States went to war with Iran. 

“You’re not going to need an exit strategy. I don’t do exit strategies,” he replied to a question about such a plan in the event of hostilities.

Senate Minority Whip Richard J. Durbin of Illinois argued there is “strong feeling that this is a historic moment, constitutionally, a historic moment for us to speak out on a war in Iran that this president could stumble into tomorrow.”

Senate Majority Leader Mitch McConnell said he “isn’t opposed” to debating that amendment, but that he would vote against it. The Kentucky Republican said he is working to try to bring the Iran amendment — and the bill itself — to a final vote this week.

“We’re very heartened by what Leader McConnell said,” Senate Minority Leader Charles E. Schumer said Tuesday. “We want to negotiate. I believe we can work all of this out.”

Having a vote on the amendment — which is sponsored by Democrats Tom Udall of New Mexico, Jeff Merkley of Oregon, Tim Kaine of Virginia and Christopher S. Murphy of Connecticut, along with Republicans Rand Paul of Kentucky and Mike Lee of Utah — may not be up to McConnell, as any one senator could object to a vote on the amendment.

“It takes one person to stop the train,” Durbin said. “But if the leader … wants to get it done, he can get it done.”

McConnell may have issues within his own caucus. Paul has already threatened to block amendments unless he receives a floor vote on two of his own, including one that would sunset the 2001 Authorization for Use of Military Force.

The House is expected to include language similar to the Senate’s Iran amendment in its defense authorization bill when it debates the measure next month, making the issue an item for conference talks on the legislation.

Meanwhile, presidential politics is throwing a wrench in the negotiations over amendments, with Schumer urging votes on Friday to allow the Democratic senators running for president to participate in debates Wednesday and Thursday and still vote on the Iran amendment and the must-pass defense measure.

“The debate is happening,” Schumer said. “I think we can do both.”

McConnell made it clear Tuesday that Democrats are going to have to filibuster the bill if they do not want final votes this week.

“Postpone legislation on our national defense to accommodate the presidential race? In the middle of this ongoing crisis overseas? Come on. Come on,” McConnell said on the floor Tuesday morning.

McConnell described his own reaction to Schumer’s request as “incredulous.”

“I’m sorry our Democratic friends feel compelled to skip out so they can compete for the favor of ‘the resistance,’” McConnell said. “The rest of us, the Republican majority — we’re going to be right here, we’re going to be right here working and voting to make America stronger and safer.”

Later in the day, he said he was “encouraged” that Schumer wants to pass the NDAA this week but said he was perplexed by Schumer’s desire for Friday votes.

Senate Armed Services Chairman James M. Inhofe said he would be “a little less charitable” to the Democrats, whom the Oklahoma Republican says are putting politics before national security.

“It’s morally wrong. It’s the most important bill of the year, and you don’t do it,” Inhofe said. “And the whole reason for delaying this thing is purely political, because these guys are running for president and they want to be on TV instead of up here doing their job.”

Delaying the vote, Iowa Republican Sen. Joni Ernst argued, would send the wrong message to U.S. adversaries.

“Iran is a threat,” Ernst said. “They are watching, make no mistake about it. We cannot play games with the National Defense Authorization Act.”

McConnell filled the amendment tree to restrict the offering of amendments to the defense bill Monday evening and also moved to limit debate on the substitute amendment from Inhofe that is now the base text.

Cameron Peters and John T. Bennett contributed to this report.