“This was a very insulting resolution, introduced by Democrats as part of a strategy to win an election on November 3 by dividing the Republican Party,” Trump said in a statement released by the White House on Wednesday.
“The few Republicans who voted for it played right into their hands.”
The Senate, where Trump’s fellow Republicans hold a 53-to 47-seat majority, is expected to hold a veto-override vote as soon as Thursday.
The resolution, which passed the House of Representatives in March and the Senate in April, was the latest effort by Congress to wrest back from the White House its constitutionally guaranteed authority to declare war.
Six Republicans in both houses supported the measure when it passed, but not enough to muster the two-thirds majority necessary in both houses to override a veto.
US-Iran tensions have risen since Trump withdrew from the 2015 nuclear deal between Tehran and world powers in 2018 and reimposed sanctions.
But Washington’s hostility skyrocketed in early January with a US drone strike that killed top Iranian commander Lt. General Qassem Soleimani.
Iran responded with a rocket attack on two military bases in Iraq housing US troops. More than 100 US troops were later diagnosed with traumatic brain injuries caused by the attack.