TORONTO (AP) — Barack Obama is urging Canadians to reelect Prime Minster Justin Trudeau, an apparently unprecedented endorsement of a candidate in a Canadian election by a former American president.

Obama tweeted Wednesday that he was proud to work with Trudeau and described him as a hard-working, effective leader who takes on big issues like climate change.

Obama says the "world needs his progressive leadership now, and I hope our neighbors to the north support him for another term."

Trudeau is in a tough re-election fight ahead of Monday's parliamentary elections.

University of Toronto history professor Robert Bothwell says an endorsement of candidate in a Canadian election by a former U.S. president has never happened before.