The House is expected to vote Thursday on legislation that would compel President Donald Trump to withdraw from the war with Iran, marking a significant test of congressional support for a conflict that began over two months ago without congressional approval.

The vote represents the latest effort by Democrats to use the War Powers Resolution of 1973 to constrain Trump's military campaigns. While previous similar votes have failed, Democrats believe they may have the support needed this time, as a small but growing number of Republicans have joined them in opposing the continued conflict.

On Tuesday, the Senate advanced its own war powers resolution when four GOP senators supported it and three others were absent. A final Senate vote could also occur Thursday, though Republican leaders expect to block it once all GOP senators are present.

Frustration with the Iran war has grown on Capitol Hill as the conflict has created a stalemate in the Strait of Hormuz, disrupting global shipping and contributing to higher gas prices in the United States. A previous House war powers resolution nearly passed last week, failing only on a tie vote after three Republicans voted in favor.

Under the War Powers Resolution of 1973, presidents have 60 days to engage in military conflict before Congress must either declare war or authorize the use of military force. Some Republicans who have previously supported Trump's efforts to target Iran's nuclear capabilities now say the president's legal timeline has expired. The White House argues the War Powers Resolution requirements no longer apply due to a ceasefire with Iran.

The legislation before the House is a concurrent resolution that would take effect without Trump's signature if passed by both chambers. However, Trump has argued that the 1973 law is unconstitutional, potentially setting up a legal challenge over congressional authority over military conflicts.