DES MOINES, Iowa — President Donald Trump and Democrat Joe Biden are assailing each other during overlapping visits to Iowa on Tuesday, previewing what the country might get in next year's election if Biden becomes his party's nominee.

Even before he left the White House, Trump unleashed a series of schoolyard taunts, declaring that "Joe Biden is a dummy." Biden quickly retorted that the president is "literally an existential threat to this country."

The back-and-forth laid bare the rising political stakes for each, even with Election Day 2020 still about 17 months away. Trump has zeroed in on Biden as a potential threat to his re-election chances and is testing themes to beat him back.

Biden, meanwhile, is campaigning as a front-runner, relishing the one-on-one fight with Trump while making sure he doesn't ignore the demands of the Democratic primary.

"I'd rather run against Biden than anybody," Trump told reporters before flying to Iowa. "I think he's the weakest mentally and I like running against people that are weak mentally."

Biden said such behavior is beneath the office of the presidency. He noted that Trump "found time to go after Bette Midler in the middle of the D-Day ceremonies," referring to the president's ongoing online feud with the actress.

Biden began the day in Ottumwa, the heart of Wapello County, a meat-packing and agricultural manufacturing center Trump was the first Republican to carry since Dwight D. Eisenhower.

It's part of Biden's dual track approach: campaigning for the caucuses while projecting himself as someone who can win in territory Trump snatched from Democrats in 2016, such as Michigan, Pennsylvania and Wisconsin.

The former vice president hit Trump on the economy — an issue the president often promotes as his chief strength in a time of low unemployment.

Biden added that Trump "backed off his threat of tariffs to Mexico basically because he realized he was likely to lose" in manufacturing states such as Michigan and Ohio.

For Trump, the biggest concern in this state dominated by agriculture interests is trade. He's beginning his trip in Council Bluffs to tour and speak at Southwest Iowa Renewable Energy, which produces and sells the corn-based fuel additive ethanol, before addressing an Iowa GOP dinner in Des Moines.

Trump is likely to try to sell farmers on the US-Mexico-Canada trade deal, which remains to be ratified by lawmakers in each country. Supporters of the deal, which is an update to the North American Free Trade Agreement, feared that Trump's recent threat to impose tariffs on Mexico over illegal immigration would jeopardize the pact's passage by US lawmakers. But Trump announced an agreement with Mexico late last week and delayed the tariffs for the time being.

The president, however, has been stung by criticism that what he announced Friday resembled steps Mexico had already agreed to take. He lashed out Monday in a pair of tweets in which he teased a secret deal with Mexico to be announced soon. Mexico countered that no secret deal was in the works.

- AP