GREEN BAY (WISCONSIN) • US President Donald Trump has revved up his campaign pitch to voters in key Rust Belt states by touting the US economy, saying he is working to stop jobs from moving to neighbouring countries and mocking his Democratic opponents.

"We're now the No. 1 economy anywhere in the world and it's not even close," he said on Saturday night at a rally in Green Bay, Wisconsin. He later told the cheering audience that returning for another term in office will make the United States stronger.

"At the end of six years, you're going to be left with the strongest country you've ever had," he said.

Mr Trump said his renegotiation of trade agreements will make the US economy stronger. He also said Japanese Prime Minister Shinzo Abe, who visited the White House last Friday, has agreed to put US$40 billion (S$54.5 billion) into the United States for new car factories.

The event was the President's first since his biggest Democratic rival, former vice-president Joe Biden, entered the 2020 race, saying in a campaign video that he is running because Mr Trump poses a threat to the nation "unlike any I had ever seen in my lifetime".

Mr Trump scheduled the rally as counter-programming to the annual White House correspondents' charity dinner in Washington. He has publicly fumed in recent weeks that reporters focused too much on unflattering episodes from Special Counsel Robert Mueller's report instead of the conclusion that his campaign had not criminally colluded with Russian efforts to disrupt the 2016 campaign.

The President renewed those complaints before a receptive crowd last Saturday, repeating his assertion that investigations into ties between his campaign and Russia amounted to a "witch hunt".

Mr Mueller's report did not find an "underlying crime" by Mr Trump related to Russian interference in the 2016 election. But the report provided an exhaustive account of Mr Trump's efforts to head off or undermine the probe, saying Congress could take action on at least 10 instances of potential obstruction of justice. Attorney-General William Barr said he determined that obstruction didn't take place.

Wisconsin will be a crucial battleground for Mr Trump, no matter who the Democrats select as their nominee. It is among a trio of Great Lake states - along with Michigan and Pennsylvania - that were thought to be reliably Democratic before Mr Trump's 2016 victory.

Despite dominant fund-raising, an established campaign organisation and the power of incumbency, Mr Trump risks losing all three states in 2020 after Republican failures in mid-term elections showed that his support in the region is fading. Any Democratic challenger will likely need to win all three to prevent Mr Trump from securing a second term in the White House.

At the rally, Mr Trump highlighted jobs being created in Wisconsin, Pennsylvania, Michigan and elsewhere, crediting the trend with his moves to rescind regulations and counter tariffs on American exports. He said he has saved "countless timber jobs", including in Wisconsin, by imposing new tariffs.

He also invoked Commerce Department data reported last Friday showing faster-than-expected growth in the US economy, and said manufacturing jobs are returning. Gross domestic product rose at a 3.2 per cent annual rate in the first quarter of 2019.

Wisconsin has earned particular notoriety after Mr Trump's 2016 opponent, former Secretary of State Hillary Clinton, did not campaign in the state during the general election. The Democratic National Committee has scheduled its 2020 convention in Milwaukee.

For Mr Trump, the state offers a potentially tricky referendum on his economic record. His administration helped Wisconsin broker a deal with Foxconn Technology Group in which the Taiwanese manufacturing giant said it would create thousands of new jobs building LCD displays in exchange for more than US$4 billion in tax breaks. The company has subsequently said it was reconsidering its plans.

Wisconsin Governor Tony Evers, a Democrat, has said the state is renegotiating the deal as Foxconn has shifted its production plans.

Wisconsin-based Harley-Davidson has also shifted some production overseas to avoid retaliatory tariffs imposed by European countries after the US hiked taxes on imported steel and aluminium. The company said in January the tariffs will cost the company between US$100 million and US$120 million this year, and reported slumping first-quarter profit last Tuesday.

Mr Trump has called the European tariffs on the motorcycle manufacturer "so unfair" and vowed retaliation in a tweet last week. White House officials have not said how or when the President will move on that threat.

On Saturday night, Mr Trump repeated names he has given to Democratic challengers. He called Mr Biden "Sleepy Joe", dubbed Senator Bernie Sanders "Crazy Bernie" and Senator Elizabeth Warren of Massachusetts "Pocahontas", in reference to her claims of Native American ancestry. He said he has no Native American blood, and that is more than she has.

BLOOMBERG