U.S. President Donald Trump on Thursday floated the idea of delaying the November presidential election, suggesting widespread voting by mail would result in a fraudulent result. 

The proposal came in a tweet, which said mail-in voting will make it "the most inaccurate and fraudulent election" in history and a great embarrassment to the U.S. -- without offering any evidence to back up the claim. 

Trump then raised the prospect of a postponement, tweeting "Delay the Election until people can properly, securely and safely vote?" 

Reaction has been swift, with even the president's top Republican allies rejecting the idea, underlining the president has no constitutional authority to change the election date, which is set by law. 

Senate Majority Leader Mitch McConnell noted the U.S. always had on-time presidential elections - "through wars, depressions and the Civil War" - while Senator Lindsay Graham simply called it "not a good idea." 

Trump's tweet came soon after the U.S. economy reported a record contraction of 32-point-nine percent in the second quarter.