WASHINGTON -- While Hillary Clinton remained the favorite to be elected president in November, the odds of Donald Trump winning the keys to 1600 Pennsylvania Ave. have increased, according to European betting houses.

London-based William Hill, whose name adorns the sports book at Monmouth Park in Oceanport, and Dublin-based Paddy Power both set Clinton's current odds to win at 8 to 15, giving her a 65 percent chance of becoming the first female U.S. president.

Trump's odds at both bookmakers were 6 to 4, giving him a 40 percent chance of winning the White House. When he first began his presidential campaign, betting houses were offering odds of 150 to 1.

Following the two national political conventions, William Hill gave Clinton odds of 4 to 11, a 73 percent chance of winning, at the beginning of August. Trump had odds of 21 to 10, or a 33 percent chance.

"The distance between the two candidates has been shortening in betting terms significantly," William Hill spokesman Graham Sharpe said.

Trump's better odds overseas mirrored his improved standing in U.S. opinion polls. She led by an average of 2.4 percentage points in head-to-head polling, according to Real Clear Politics. Statistics expert Nate Silver's fivethirtyeight.com gave her a 69 percent chance of winning the presidency.

Paddy Power spokesman Feilim Mac An Iomaire said Trump's odds surged in the last 24 hours following reports that Clinton had pneumonia.

"Republicans have been pushing the ill-health agenda for some time and there's no doubt that Hillary's pneumonia will be used to attack her," he said.

Jonathan D. Salant may be reached at jsalant@njadvancemedia.com. Follow him on Twitter @JDSalant. Find NJ.com Politics on Facebook.