The House is preparing to vote Thursday on a war powers resolution to halt President Donald Trump's attack on Iran, a sign of unease in Congress over the rapidly widening conflict that is reordering U.S. priorities at home and abroad.

It's the second vote in as many days, after the Senate defeated a similar measure along party lines. Lawmakers are confronting the sudden reality of representing the American people in wartime and all that entails — with lives lost, dollars spent and alliances tested by a president's unilateral decision to go to war with Iran.

The tally in the House is expected to be tight, but the outcome will provide an early snapshot of the political support, or opposition, to the U.S.-Israel military operation and Trump's rationale for bypassing Congress, which alone has the power to declare war.

"Donald Trump is not a king, and if he believes the war with Iran is in our national interest, then he must come to Congress and make the case," said Rep. Gregory Meeks, the top Democrat on the House Foreign Affairs Committee.

Meeks said in his nearly three decades in Congress, the hardest votes he has taken have been deciding whether to send U.S. troops to war.

The roll calls are a clarifying moment for the president and the parties just days into the overseas conflict that has quickly carried echoes of the long U.S. wars in Afghanistan and Iraq. Many veterans of those wars have since run for office and now serve in Congress.

Trump's Republican Party, which narrowly controls the House and Senate, largely sees the conflict with Iran not as the start of a new war, but the end of a regime that for decades has long menaced the West. The operation has killed Iran's Supreme Leader Ayatollah Ali Khamenei, which some view as an opportunity for regime change, though others warn of a chaotic power vacuum.

Rep. Brian Mast of Florida, the GOP chairman of the House Foreign Affairs Committee, publicly thanked Trump for taking action against Iran, saying the president is using his own constitutional authority to defend the U.S. against the "imminent threat" the country posed.

Mast, an Army veteran who worked as a bomb disposal expert in Afghanistan, said the war powers resolution was effectively asking "that the president do nothing."

For Democrats, Trump's war with Iran, influenced by Israeli Prime Minister Benjamin Netanyahu, is a war of choice that is testing the balance of powers in the U.S. Constitution.

"The framers weren't fooling around," said Rep. Jamie Raskin, D-Md., arguing that the Constitution is clear that only Congress can decide matters of war.

He said whether lawmakers support or oppose the Trump administration's military action, they should have the debate. "It's up to us, we've got to vote on it."

While views in Congress are largely falling along party lines, there are crossover coalitions. Both the House and Senate resolutions were bipartisan, and are drawing bipartisan support and opposition. The House is also voting on a separate resolution affirming that Iran is the largest state sponsor of terrorism.

The war powers resolution, if signed into law, would immediately halt Trump's ability to conduct the war unless Congress approved the military action. The president would likely veto the measure.

As an alternative, a small group of Democrats has proposed a separate war powers resolution that would allow the president to continue the war for 30 days before he must seek congressional approval. It is not expected to come yet for a vote.

After launching a surprise attack against Iran on Saturday, Trump has scrambled to win support for a conflict that Americans of all political persuasions were already wary of entering. Trump administration officials spent hours behind closed doors on Capitol Hill this week trying to reassure lawmakers that they have the situation under control.

Six U.S. military members were killed over the weekend in a drone strike in Kuwait, and Trump has said more Americans could die. Thousands of Americans abroad have scrambled for flights, many lighting up the phone lines at congressional offices as they sought help trying to flee the Middle East.

Defense Secretary Pete Hegseth said that the war could extend eight weeks, twice as long as the president first estimated. Trump has left open the possibility of sending U.S. troops into what has largely been a bombing campaign by air. Hundreds of people in the region have died.

The administration said the goal is to destroy Iran's ballistic missiles that it believes are shielding its nuclear program. It has also said Israel was ready to act against Iran, and American bases would face retaliation if the U.S. did not strike first. On Wednesday, the U.S. said it torpedoed an Iranian warship near Sri Lanka.