The trip to Eau Claire in Wisconsin followed by a stop in Detroit later on Wednesday is part of the introductory campaign swing for Walz, the governor of nearby Minnesota. Harris named Walz as her vice presidential pick on Tuesday in the biggest political decision of her nascent White House bid, which has energised Democrats and shaken up the race.
The selection of Walz - an Army National Guard veteran and former teacher and football coach - adds geographic balance to a ticket with a Californian at the helm who needs a strong showing in the Midwest to win the November 5 election against Republican rival Donald Trump.
Democratic presidential nominee Vice President Kamala Harris received a warm welcome in Wisconsin. (AP PHOTO)
A former congressman who won elections in a Republican-leaning district before becoming governor, Walz has a record of appealing to the white, rural voters who have increasingly turned to Trump over the years.
Trump and his running mate, Senator JD Vance of Ohio, have rushed to portray Walz as too left-wing, echoing their criticisms of Harris.
In an interview on Fox News on Wednesday, Trump called Walz a "radical" liberal and said he was "thrilled" Harris had picked him.
Trump also said he would debate Harris in the "pretty near future" and that details would be announced soon. He said his preference was for Fox to host the debate.
Republican vice president nominee JD Vance inspected the incumbent vice president's plane. (AP PHOTO)
Last week, Trump proposed a debate with Harris on Fox News on September 4. The Harris campaign said Trump was trying to back out of a debate that had already been set with ABC on September 10.
In an unusual moment on Wednesday, Vance approached Air Force Two while Harris appeared to be in her motorcade on the tarmac in Wisconsin. He asked reporters nearby why she didn't take more of their questions.
The two candidates' planes were several hundred yards from one another at Chippewa Valley Regional Airport in Eau Claire.
Vance said he was trying to "check out this plane that's going to be mine in a few months" and briefly spoke to reporters while Harris' motorcade drove away, video taken by local reporters showed.
In Detroit, Vance tried out some attack lines on his Democratic counterpart, criticising Walz's handling of the protests in Minneapolis following the killing of George Floyd there by police in 2020.
Critics have accused Walz of being too slow to mobilise law enforcement to stop looting, arson and violence that accompanied the protests. Walz's aides have pushed back against the charge, saying he deployed the National Guard to respond to the protests.
"He allowed rioters to burn down Minneapolis," Vance said.
Minnesota Governor Tim Walz's nomination for vice president has reinvigorated the Democratic party. (AP PHOTO)
Leading civil rights advocates, however, have credited Walz for his decision to have Minnesota's attorney general lead the prosecution of the police officer who was convicted of murdering Floyd.
Vance, who served in the Marine Corps and was a public affairs officer during a six-month stint in Iraq, also slammed Walz's military record, saying he abandoned his National Guard battalion right before its deployment to Iraq in 2005. Walz, who served in the Guard for 24 years, retired to run for Congress.
Democrats regard Wisconsin and Michigan as near must-wins in the 2024 election. The states have loomed large for the party since Hillary Clinton's unexpected defeats there helped clinch Trump's 2016 win.
Biden beat Trump in both states in 2020. But opinion polls showed him facing a close battle in Michigan before he dropped out of the race last month, with much of the state's significant Arab and Muslim American population fuming over his administration's support for Israel in its war against Hamas in Gaza following the October 7 attacks.
The Democratic candidates are expected to travel in coming days to more than a half dozen states likely to determine the winner of the election.
At the pair's first rally together on Tuesday night in Philadelphia, Harris devoted much of her speech to highlighting Walz's background as a small town native, a high school social studies teacher and football coach and a Guard member.
Walz, a folksy, affable speaker, nevertheless did not hold back on Trump and Vance, repeating his viral comment that they are "weird" and criticising them over abortion, crime and the economy.
