Several lawmakers are worried that the Trump administration will seek to use an old authorisation for war issued by Congress in 2001, following the September 11, 2001 terrorist attacks against the US. It gave former president George W Bush the power to retaliate against al-Qaeda.
Testifying before Congress in May, Mike Pompeo, secretary of state, said there was "no doubt" that a link existed between al-Qaeda and Iran, accusing the Islamic republic of harbouring al-Qaeda terrorists.
He declined to say, however, whether he thought the administration had the legal authority to engage in war with Iran based on the 2001 authorisation, saying he would leave the question to lawyers.
Senator Tom Udall, one of the sponsors of the Senate measure on Iran, said the Senate had sent a "clear message" to Trump, even though the measure was blocked. It needed 60 votes to advance, but only received 50.
"House and Senate leaders must recognise the will of Congress and include a strong provision to bar an unauthorised war with Iran in the final version of the defence bill that comes out of conference," said Udall.
Written by: Aime Williams
© Financial Times 2019