The Associated Press photos / President Donald Trump holds up a signed executive order to streamline the approval process for GMO crops, after speaking at Southwest Iowa Renewable Energy in Council Bluffs, Iowa, on Tuesday.

MOUNT PLEASANT, Iowa — President Donald Trump and Democrat Joe Biden assailed 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 “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.

“I hope his presence here will be a clarifying event because Iowa farmers have been crushed by his tariffs toward China,” Biden said. “It’s really easy to be tough when someone else absorbs the pain, farmers and manufacturers.”

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 headed to Council Bluffs and Southwest Iowa Renewable Energy, a facility that produces and sells the corn-based fuel additive ethanol, touring a grain receiving station and an area for drying cornmeal among mountains of corn and humming machinery.

“I fought very hard for ethanol but you proved me right,” Trump said, adding that he fought “for the American farmer like no president has fought before.” But he then again mocked Biden while chiding former President Barack Obama, saying “America must never again be held hostage to foreign suppliers as we were under the Obama-Biden, Sleepy Joe group.”

“He was some place in Iowa today,” the president said of the former vice president “and he said my name so many times that people couldn’t stand it.”