Congress will vote this week on whether to authorize President Donald Trump's war in Iran. It may not matter, experts say.

The US Constitution gives US Congress the power to declare war, but in practice modern presidents launch military campaigns first and lawmakers debate them later.

Top Capitol Hill Democrats, and a small number of Republicans, watched in alarm Saturday as the administration launched a major US assault on Iran, decrying President Donald Trump’s call for the overthrow of another foreign government without their expressed approval.