"People don't respect him", Mr Trump said of Mr Biden after touring a renewable energy facility in Council Bluffs.
"I'd rather run against Biden than anybody", Trump told reporters before flying to Iowa.
Trump in recent days has lashed out at the New York Times in the wake of a report that he was briefed on a 17-state poll conducted by his campaign pollster, Tony Fabrizio, that showed him trailing Biden in numerous states he needed to win in 2020.
He started to say more but then stopped himself, quipping: "My mother would say: "Joey, focus".
Showing on CNN, Axelrod cautioned that Biden's mild campaign schedule, when compared to those of other competitors in the Democratic field, left him open to such criticisms. He also launched the Biden Cancer Initiative after leaving the office.
Biden went on to declare, "President Trump has committed gross abuses of power like using the IRS to silence political opponents, making laws through executive action, and unleashing federal agencies to spy on opposition candidates, or maybe that was Obama but anyway it was one of those presidents and it's got to stop". "Warning of the influence it's had on American farmers and producers, Biden plans to name Trump an "existential menace" to the nation.", Donald Trump and I are each in Iowa at present.
Biden began the day Tuesday in Ottumwa, the heart of Wapello County, a meat-packing and agricultural manufacturing center that Trump was the first Republican to carry since Dwight D. Eisenhower. 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. He thinks that being tough is great, well it's really easy to be tough when someone else absorbs the pain: "farmers, manufacturers, the automobile industry", Biden said.
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 MI and Ohio.
The Democratic frontrunner took some shots at President Trump while campaigning in Iowa, calling him an "existential threat" to the country.
"That's why I've worked so hard in my career to make sure that".
But he then mocked Mr Biden again.
Biden did spend some time talking about his policies like his pledge to either support or oppose the Hyde amendment, and his sense that China either was or wasn't a threat to America, whichever you prefer. "It depends on which race they're running".