Donald Trump had an explosive argument with Republican senators during a private meeting in Washington, D.C. on Wednesday over limitations on his powers to direct the war with Iran.The Republican-controlled Senate passed bipartisan legislation ordering Trump to end the war with Iran or seek congressional approval to continue it. Their move marks the most significant Republican rebuke of the President to date, and a sign of the widening rift between him and his party.Trump met privately with the entire Republican Senate majority behind closed doors on Capitol Hill, demanding to know why they had decided to limit his power to wage war. Senator Bill Cassidy of Louisiana attempted to explain their rationale, but the President immediately resorted to personal insults. Cassidy is one of the four Republican senators, including Susan Collins, Lisa Murkowski, and Rand Paul, who joined Democrats in the war powers vote. 'He [Trump] was asking why anybody would vote for the power's accident. I said, "Is that a rhetorical question, or do you want to know?" He goes, "I want to know."' Cassidy told the Daily Mail. Cassidy began 'yelling' at the President at one point, and Trump responded by calling him a lunatic and telling him to 'sit down.' The Republican lawmaker refused and referred to Trump as 'brother.' The President told him he wasn't his 'brother' before Cassidy eventually settled back into his seat.Trump also mocked the senator for losing his primary, which the senator perceived as the President's attempt to bully him. The Republican-controlled Senate passed bipartisan legislation ordering Trump to end the war with Iran or seek congressional approval to continue it Trump met privately with the entire Republican Senate majority behind-closed doors on Capitol Hill to discuss why they had decided to vote to limits his power to wage war Senator Bill Cassidy of Louisiana attempted to explain their rationale, but the President immediately resorted to personal insultsCassidy lost his Republican primary in May, and will leave the Senate in January, making him the first elected incumbent senator to lose a primary since 2012.'I'm not going to be bullied when I feel like I'm asking a question the American people need to know. And so, at that point, it began to escalate,' Cassidy told the Daily Mail.Trump's meeting with the senator followed his controversial decision to abruptly cancel a signing ceremony for a bipartisan housing bill. The President said he would not sign the bill until the Senate passed his controversial Save America Act, which requires Americans to present a voter ID to cast an electoral ballot.