Donald Trump has struggled in the polls since the Democratic National Convention. Associated Press/David Zalubowski Donald Trump's comments this week that President Obama "founded" the Islamic State and that Second Amendment advocates can "do something" about rival Hillary Clinton were terrible for his campaign, according to bookmakers.

Trump's odds have fallen to an average of 12/4, down from 5/2 just two days ago. This gives him just a 25% chance of winning. Clinton, meanwhile, is riding high with average odds of 2/8.

Trump's comments this week have been strong, even by his own standards

At a rally in North Carolina on Tuesday, he said that a Clinton win would mean she could pick her own Supreme Court judges at will. He then added:

"Hillary wants to abolish, essentially abolish, the second amendment. If she gets to pick her judges, nothing you can do, folks. Although the Second Amendment people, maybe there is, I don’t know. But I’ll tell you what, that will be a horrible day."

The Second Amendment, of course, is the constitutional right for Americans to "bear arms," and Trump's comments have been seen by some as a suggestion that he is encouraging gun violence.

Immediately after Trump's comment, Democrats reacted angrily, saying Trump implied that Clinton should be assassinated. Sen. Chris Murphy of Connecticut tweeted: "Don't treat this as a political misstep. It's an assassination threat, seriously upping the possibility of a national tragedy & crisis."

Trump eventually responded that the media was exaggerating his remarks, telling Fox News host Sean Hannity he was was simply talking about political action rather than violence: "This is a political movement. This is a strong, powerful movement, the Second Amendment. There can be no other interpretation. I mean, give me a break."

Despite the uproar surrounding the comments, it seems Trump could not help going further just a day later.

Speaking at another campaign rally in Florida on Wednesday, Trump called President Obama the founder of ISIS and "crooked" Clinton the co-founder. He said that the Islamic State "honours" Obama, and that "in many respects ... ISIS is honoring President Obama — he is the founder of ISIS."

Graham Sharpe from William Hill said while Trump's campaign has often benefited from his shocking comments, his recent behaviour was going too far for many voters. But he added that a Trump win would cost bookmakers a lot of money:

"With hefty support coming in for Clinton, and Trump taking a PR pasting for recent remarks, his odds have drifted to their longest level for some three weeks. However, Trump remains significantly the worst result for us, and we'll face a six figure loss should he triumph."

Here are Clinton and Trump's current odds to win the US presidential race: