The US Senate opened debate on a resolution to limit President Donald Trump's authority to go to war with Iran, with passage likely after eight Republicans sided with Democrats to advance the bill.
A vote on the war powers resolution could take place as early as Thursday, amid concerns that Trump could embark on open military conflict with Tehran without consulting Congress.
Passage could embarrass the president, who has been able to count on the Republicans' solid majority in the Senate to block legislation he disagrees with.
While Trump is expected to veto the legislation, he warned the Senate on Wednesday to vote it down and not limit his policy choices.
"It is very important for our Country's SECURITY that the United States Senate not vote for the Iran War Powers Resolution," he tweeted.
"We are doing very well with Iran and this is not the time to show weakness... If my hands were tied, Iran would have a field day. Sends a very bad signal. The Democrats are only doing this as an attempt to embarrass the Republican Party."