Toronto, Canada - The Democratic Senate candidate in Michigan on Wednesday charged that President Donald Trump is blocking the opening of a new US-Canada bridge as a favor to a major donor.

The allegation made public by Mallory McMorrow began circulating months ago, shortly after Trump leveled apparently misleading claims surrounding construction of the $4.7-billion Gordie Howe International Bridge, which connects Detroit and Windsor, Ontario.

Canadians thought the spat had been resolved when Prime Minister Mark Carney announced on June 9 that the bridge would officially open in three days.

But Carney backtracked two days later, saying the ceremony had been called off "at the request of the United States."

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In a campaign ad and press release on Wednesday, McMorrow said Trump was acting on behalf of Matthew Moroun, a billionaire who donated $1 million to a pro-Trump political action committee, MAGA Inc.

Moroun's family controls the Ambassador Bridge, which has connected the auto hubs of Detroit and Windsor for decades.

"The Gordie Howe Bridge is finished, but Donald Trump won't open it, because the billionaire family that owns the other bridge gave him a million bucks.

"I'm Mallory McMorrow and I've got one message for the president: Open this damn bridge," the Democratic Senate hopeful says in the ad, as she walks the banks of the Detroit River.

"The Trump administration is blocking it from opening, trying to shake down Canadian politicians and the state of Michigan," McMorrow's campaign said in a press release.

Trump's February Truth Social post condemning the Gordie Howe Bridge came as a surprise to many in Canada and the nature of his concern about the structure was not entirely clear.

He charged that it was built with almost no US materials and that he wouldn't allow it to open until it was "at least half" US-owned.

According to a fact sheet issued by the Windsor-Detroit Bridge Authority, the bridge was financed entirely by Canada and will be jointly owned by Canada and the state of Michigan.

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The New York Times reported in February that Trump criticized the Gordie Howe Bridge shortly after a meeting between Moroun and US Commerce Secretary Howard Lutnick.

It is named after late Canadian-born National Hockey League great and Detroit Red Wings star Gordie Howe, in what was meant to be a symbol of unity between Canada and the US.