US President Donald Trump pronounced "the Russia hoax finally dead" before launching into signature issues such as immigration and trade in a campaign speech in Michigan on Thursday evening.

"After three years of lies and smears and slander, the Russia hoax is finally dead," Trump proclaimed to an audience at the Van Andel Arena in Grand Rapids. "The collusion delusion is over. This was nothing more than a sinister effort to undermine our historic election victory."

On Sunday, US Attorney General William Barr released a summary of Special Counsel Robert Mueller's more than 300-page report about his investigation into Russia's influence in the 2016 presidential election. The investigation did not find that members of Trump's campaign conspired with Russia during the campaign.

"Robert Mueller was a god to the Democrats. He was a god to them until he said 'no collusion.' They don't like him so much now."

Trump said that when people started asking him about Russia, he said, "What the hell does Russia have to do with my campaign?

"This group of major losers did not just ruthlessly attack me, my family, and everyone who questioned their lies. They tried to divide our country, to poison the national debate and to tear up the fabric of our great democracy," Trump said.

Grand Rapids also was the site of Trump's final campaign rally before his victory in 2016. Michigan was one of three key states — along with Pennsylvania and Wisconsin — that delivered his victory over Democrat Hillary Clinton.

Trump could face a tougher road in those states in 2020. Republicans lost badly in November's midterm elections, and according to a Federal Reserve measure of state-level economic performance, Michigan and Pennsylvania trail the US overall.

In Wisconsin, where economic conditions have kept pace with US growth, Trump's approval rating is below 50 percent.

"A lot of these blue-collar Democrats do feel that the president has stopped the US from getting sand kicked in its face," said John Brabender, a Republican consultant who works on campaigns in Pennsylvania. "But these are incredibly fluid voters, and the race will probably come down to them once again. If those Democrats switch back in places like Pennsylvania and Michigan, it's going to be really hard for the GOP to hold onto the White House."

Being in Michigan, Trump focused on the auto industry. He chastised GM over its announced plant closures in Michigan and Ohio.

"Get the damn plants open, get 'em open now," Trump said, pointing out that foreign automakers such as Toyota and Volkswagen were expanding in the US.

"We think General Motors will still be doing the same," he said.

"Under my administration, we live by two simple rules: Buy American and Hire American."

Trump pivoted to one of his signature campaign issues — Mexico and the southern border.

"Mexico took about 30 percent of your car business," he told the audience. "If we close the border, that means we're not taking those cars into the country. That means we're going to make a lot more cars here in the good old USA.

"We will close the damn border," Trump said, drawing shouts of "USA!, USA!" and "Build the wall!"

Trump praised Immigration and Customs Enforcement (ICE) as "great American patriots" and said that some Democrats want to abolish ICE.

"We want our country to be a sanctuary for law-abiding Americans, not for criminal aliens," Trump said.

The president said that "300 Americans a week die by Mexican-trafficked heroin".

Reuters and Bloomberg contributed to this story.