A handful of Republican senators ignored Donald Trump's warnings about a Democratic-crafted measure designed to limit his ability to go to war with Iran.

The upper chamber passed the bill, authored by Senator Tim Kaine, with all 43 Democrats in support and eight Republicans joining them. Senators were both concerned that Mr Trump's killing of a top Iranian general – whom they all agree was a terrorist leader – was too brazen and that Congress since 9/11 has given too many war powers to the executive branch.

Senators Lamar Alexander, Susan Collins of Maine, Lisa Murkowski of Alaska, Todd Young of Indiana, Mike Lee of Utah, Rand Paul of Kentucky and Jerry Moran of Kansas defied Trump's call that GOP senators kill the bill before it could reach the House, where it is expected to pass.

Mr Trump issued a warning to GOP senators on Wednesday afternoon.

"We are doing very well with Iran and this is not the time to show weakness. Americans overwhelmingly support our attack on terrorist Soleimani...." Mr Trump tweeted ahead of a procedural vote on the measure, referring to Maj Gen Qassem Soleimani, head of the Iranian Revolutionary Guard's Quds Force he ordered killed earlier this year. (The Trump administration has deemed the IRG a terrorist organisation, which was part of their argument he has ample legal authorities to order such strikes -- echoing the Bush 43 and Obama administrations.)

"...If my hands were tied, Iran would have a field day," Mr Trump wrote in a second tweet. "Sends a very bad signal. The Democrats are only doing this as an attempt to embarrass the Republican Party. Don't let it happen!"



The measure was written by Senator Tim Kaine of Virginia, the Democratic vice presidential nominee in 2016.

"The resolution underscores that Congress has the sole power to declare war, as laid out in the Constitution," Mr Kaine said in a statement. "The resolution will force a public debate and vote in Congress as intended by the framers of the Constitution to determine whether United States forces should be engaged in these hostilities."

Mr Kaine, a member of the chamber's Foreign Relations Committee, crafted his measure after Mr Trump ordered the killing of Soleimani, just the latest action by two presidents that have worried Mr Kaine about Congress giving up its constitutional war-making authorities, a decades-long trend.

The White House used that designation and the office of the president's Article II powers to defend the country against all threats as legal justification for taking out the Quds leader, backed by most Republicans on Capitol Hill.

Senate Majority Leader Mitch McConnell kept most of his caucus in line – ensuring an expected veto from Mr Trump would not be overridden – voiced his opposition to the Kaine measure earlier this week, which he deemed "deeply flawed on a number of levels," a signal to his caucus that he wants it to fail.