The U.S. Senate is preparing to hold a vote on Wednesday that could potentially block President Donald Trump from using further military force against Iran. This comes amid shifting messaging from the administration about the recent strikes and warnings about more American casualties to come.

Background on the War Powers Resolution

This is the second time in less than a year that Democratic Senator Tim Kaine of Virginia has pushed for a vote on a war powers resolution related to Iran. The upper chamber previously voted down a similar effort in June, following the U.S. bombing of three locations central to Iran’s nuclear program.

Kaine’s resolution, co-sponsored by Republican Representative Rand Paul of Kentucky, would direct the removal of U.S. Armed Forces from hostilities within or against the Islamic Republic of Iran that have not been authorized by Congress.

The war powers vote was expected ahead of the strikes on Iran that began on Saturday, but the massive military operation has increased the stakes and urgency of the vote. Senate Minority Leader Chuck Schumer, a New York Democrat, expressed concerns about mission creep, stating, ‘They have shifting goals, different goals all the time, different answers every day. And I am truly worried about mission creep.’

Political Dynamics and Legislative Challenges

With a 53-seat Republican majority, the resolution appears unlikely to pass, as it would require a simple majority to advance the measure. Democratic Senator John Fetterman of Pennsylvania has pledged to vote against the resolution, meaning it would need at least four other Republicans in addition to Paul to pass.

In June, the Iran war powers resolution received support from most Democrats and Paul, while Fetterman voted with most Republicans against it. Even if both chambers were to approve the resolution, the outcome would be largely symbolic, since the president could simply veto the resolution. Democrats would need two-thirds majorities in both the House and Senate to override his veto.

Kaine acknowledged during a call with reporters that the renewed effort is unlikely to pass, but he emphasized the importance of having members of Congress on the record about the war with Iran. ‘If you don’t have the guts to vote yes or no on a war vote, how dare you send our sons and daughters into war where they risk their lives,’ Kaine said.

Public Opinion and Congressional Concerns

A CBS News poll found that most Americans disapprove of the war with Iran and believe the Trump administration has not clearly explained its goals. About half of Americans think the war could last months or years.

During a classified briefing with Trump administration officials on Tuesday, Democrats expressed dissatisfaction with what they heard. Senator Chris Murphy of Connecticut said, ‘They told us in there that this is an open-ended operation that hasn’t even really started in earnest yet. There will be more Americans killed. They refuse to take off the table, the insertion of ground troops.’

Senator Cory Booker of New Jersey added, ‘There clearly was no imminent threat.’

Senate Majority Leader John Thune, a South Dakota Republican, defended the administration’s actions, stating they are ‘consistent with what previous administrations have done’ in prior conflicts. Thune added that ‘the president was perfectly within his rights to take the steps that he took.’

The Constitution grants Congress the authority to declare war. In response to the Vietnam War, Congress passed the 1973 War Powers Resolution as a check on the president’s power to enter armed conflict without consent from the legislative branch. The law requires the president to consult with Congress in ‘every possible instance’ ahead of the introduction of any military forces and to report to Congress within 48 hours of deploying forces if Congress hasn’t authorized a declaration of war, and caps any unauthorized engagement at 60 days.

Secretary of State Marco Rubio stated that ‘no presidential administration has ever accepted the War Powers Act as constitutional’ and added that ‘all that said, we complied with the law 100%, and we’re going to continue to comply with it.’

In a notification to Congress, Trump cited ‘repeated efforts to achieve a diplomatic solution to Iran’s malign behavior’ but said ‘the threat to the United States and its allies and partners became untenable.’

Kaine said he could continue forcing votes on the issue in the coming weeks, adding that some of his Senate colleagues who initially vote against the resolution could flip their votes as the situation with Iran develops. He noted that several Republicans eventually helped advance a war powers resolution related to Venezuela earlier this year, shortly after the U.S. military captured former President Nicolás Maduro, over concerns about the potential for U.S. troops to be deployed there and Trump’s comments about running Venezuela. The effort, however, stalled after the Trump administration put pressure on several of the holdouts to flip their votes.

Republican Senator Josh Hawley of Missouri, who once supported limiting the president’s ability to strike Venezuela, said he believes the Trump administration is in compliance with the law on Iran and intends to vote against the war powers resolution. ‘My view has always been, ground troops will require congressional authorization,’ Hawley said Tuesday.

Last year’s efforts to curtail involvement in Iran also fizzled out after it was clear the U.S. involvement in the 12-day war between Iran and Israel was limited, and a ceasefire was reached.

The Senate vote comes ahead of a vote expected in the House on a similar resolution later this week.