Prime Minister David Cameron's plans for joining a looming military strike on Syria were in disarray on Thursday after a revolt by lawmakers warning him to heed the "lessons of Iraq".

After imploring the world not to stand idly by over Syria's suspected use of chemical weapons, Cameron was forced into an awkward climbdown on Wednesday when the opposition Labour party as well as lawmakers in his own Conservative party said they wanted more evidence before voting for military action.

On Thursday, Cameron's government published legal advice it had been given which it said showed it was legally entitled to take military action against Syria even if the United Nations Security Council did not approve such action....

More than 100 House lawmakers — at least 98 Republicans and 18 Democrats — have signed on to a letter formally requesting that President Obama seek congressional approval for any military response to the use of chemical weapons in Syria.

The letter, first written by Rep. Scott Rigell (R-Va.), suggests that failure to seek congressional authorization for military strikes would be unconstitutional. (Read more about the letter in this previous Post Politics report.)

“I’m grateful and encouraged by the strong, bipartisan support this letter has received,” Rigell said in a statement Wednesday. “It’s a clear indication that this issue is not personal to the president, but rather represents common ground in Congress and a deep respect for the Constitution.”

The request by hundreds of lawmakers came as House Speaker John A. Boehner (R-Ohio) also formally requested in a letter that Obama “provide a clear, unambiguous explanation of how military action — which is a means, not a policy — will secure U.S. objectives and how it fits into your overall policy” regarding the situation in Syria....