LA CROSSE, Wis. — For a few hours, the unofficial Labor Day start to the fall presidential campaign centered around Wisconsin, as Vice President Mike Pence tried to poach Democrats in this Mississippi River town and Senator Kamala Harris sought to rally the Democratic base in Milwaukee.
But their dueling events at opposite ends of this increasingly pivotal state — as well as Joseph R. Biden’s visit to another battleground, Pennsylvania — were soon overwhelmed by a force as strong as any current: President Trump’s thirst for attention.
The only member of the two tickets not to be on the campaign trail Monday, Mr. Trump abruptly called a White House news conference and then used it to air a range of personal and political grievances. He called his opponents names — Mr. Biden was a “stupid person” and Ms. Harris was “not a competent person.” Yet more notable than his usual partisan insults was his extraordinary attack on the country’s senior military officials.
Defending himself for a fifth straight day following a report in The Atlantic that he ridiculed America’s war dead, Mr. Trump suggested the accusations came from Pentagon leaders, whom he described as war profiteers.
“They want to do nothing but fight wars so that all of those wonderful companies that make the bombs, that make the planes, that make everything else, stay happy,” Mr. Trump said of the officers he commands, making no mention of his own choice for defense secretary, Mark T. Esper, who was an executive at the defense contractor Raytheon.
The broadside, coming after current and retired officers have been notably quiet about claims that the president described those killed in action as “losers,” only added more fuel to an explosive story line that many Republicans want Mr. Trump to put behind him.
For the purposes of the campaign, Mr. Trump’s preoccupation with the Atlantic article illustrated the limited value of the presidential bully pulpit in the hands of a candidate unwilling to drive a focused message.
Monday, after all, was poised to showcase a showdown between Mr. Pence and Ms. Harris, who were appearing together for the first time in the same state on the same day.
The vice president, joined by Labor Secretary Eugene Scalia, was hoping to appeal to the white working-class voters along the state’s western border who supported Democrats for a generation before helping tip the state to Mr. Trump by less than a percentage point in 2016.
Standing before a group of employees at a regional utility company, Mr. Pence trumpeted the administration’s work on behalf of dairy farmers, claimed credit for the state’s booming economy before the coronavirus crisis and repeatedly attacked Mr. Biden and Ms. Harris by name.
Noting that Ms. Harris was one of only 10 senators to oppose the renegotiated North American free trade pact, because it did not do enough to address climate change, the vice president argued that she had put a “radical environmental agenda ahead of Wisconsin dairy and ahead of Wisconsin power.”
Though the company they spoke at employs some union members, neither Mr. Pence nor Mr. Scalia alluded to organized labor in their remarks, a reflection of their roots on the right but a notable decision given Mr. Trump’s strength in some union households.
Mr. Pence used the start of his speech to claim that Mr. Biden would perpetuate “policies that have literally led to violence in our major American cities,” reprising the Republican attack line that Democrats would preside over a dangerous, lawless nation.
Mr. Pence also scorned Mr. Biden for not criticizing Democratic mayors or mentioning the far-left group Antifa by name in his condemnations of violence.
While he acknowledged that the use of force by law enforcement should be “thoroughly investigated,” Mr. Pence did not refer to the police shooting of Jacob Blake, instead focusing on the violent aftermath of the shooting in Kenosha, Wis., much as Mr. Trump did in his visit there last week.
In his own trip there last week, Mr. Biden met with the Blake family, as Ms. Harris did Monday upon arriving in Milwaukee.
She also met with union workers as well as Black business owners and pastors in the city, where Democratic turnout dipped four years ago and aided Mr. Trump’s victory.
“We have to get this done, I need your help in Milwaukee,” Ms. Harris told supporters lined up to greet her on the sidewalk, encouraging them to participate in early voting.
Even before the events in Kenosha, the state’s evenly divided politics and Mr. Trump’s need to keep his 2016 map largely intact were already thrusting Wisconsin to the center of this year’s race.
After Hillary Clinton memorably failed to campaign here four years ago, Mr. Biden last week chose Wisconsin as his first Midwestern campaign stop after the Democratic convention, and he has assured local party leaders that he will return regularly.
Desperate to keep Wisconsin in their column, local Republicans this summer sought to put the rapper Kanye West on the state’s ballot in hopes he could drain votes from Mr. Biden and make it easier for the president to win with less than a majority, as Mr. Trump did four years ago. But they were late filing paperwork for Mr. West and are now in court appealing the decision to keep him off the ballot.
More recently, as Mr. Pence demonstrated Monday, Republicans have tried to elevate law-and-order issues to make up ground against Mr. Biden in Wisconsin.
The former vice president has responded by airing a commercial, here and in other swing states, that features footage from a speech he delivered last week in Pittsburgh, in which he pointedly denounced violent protests.
There’s no evidence yet that the effort to portray Mr. Biden as soft on crime is cutting into his advantage: He has enjoyed a steady lead in Wisconsin polls for months, including those taken in the aftermath of the Kenosha unrest.
Comparing this election with the one in 2016, when third-party candidates captured more than 6 percent of the vote in Wisconsin and an unusually large number of voters said they were undecided in final days of the election, Charles Franklin, a Marquette University pollster, said the current race was far more stable.
“You’ve got a smaller third-party share and a smaller pool of people still to break so that makes it less uncertain going into the last 60 days,” said Mr. Franklin, whose surveys show about half as many undecided voters as he found four years ago.
Mr. Trump’s overall margin in Wisconsin four years ago was less than 23,000 votes, lower than the total number of votes cast for third-party candidates in Milwaukee County alone that year.
Still, the 2016 results and a similarly narrow win in 2018 by the Democratic governor, Tony Evers, make clear that Wisconsin is poised to have the sort of knife’s-edge race that characterized presidential elections in the state before former President Barack Obama’s two sizable victories.
A victory by Mr. Biden here would be a significant blow to Mr. Trump’s Electoral College calculus. If the president were to hold every other state he captured in 2016, he’d need to win at least one of three crucial swing states to claim re-election: Michigan, Pennsylvania and Wisconsin. With his campaign increasingly concerned about Michigan, where it has cut its advertising, Wisconsin and Pennsylvania loom even larger.
Not coincidentally, Pennsylvania is where Mr. Biden was on Labor Day.
His day reflected the traditional spirit of the holiday in Democratic politics, minus the parade routes and union-hall gatherings where Mr. Biden has been a fixture for decades. They were canceled this year because of the pandemic.
At a stop in Lancaster, Pa., Mr. Biden promised that he would be “the best friend labor has ever had in the White House” and criticized Mr. Trump for treating the stock market as representative of the whole economy.
Later in the day, at a virtual event with Richard Trumka, the A.F.L.-C.I.O. president, in Harrisburg, Mr. Biden attacked the president for presiding over the huge job losses during the pandemic and promised that his administration would “put people to work right away” with a large-scale infrastructure program. Union members, he said, “deserve a president who fights like the devil for you.”
But Mr. Biden, too, returned to the subject of Mr. Trump’s respect for the military — “none of the veterans you know are losers,” he said — and accused the president of failing to appreciate not only soldiers but also a larger community of workers who believe in self-sacrifice.
“He’ll never understand you,” Mr. Biden told the online audience of union members, adding, “He’ll never understand our cops, our firefighters.”
Turning more personal, he used an interview with a Pennsylvania television station to rebut Mr. Trump’s claims that was on the decline. “Watch how I run up ramps and how he stumbles down ramps, OK?” Mr. Biden said.
At his news conference, Mr. Trump leveled attacks of his own against Mr. Biden, often in scattershot terms.
And instead of focusing on Friday’s jobs report, which showed unemployment falling, Mr. Trump vented about other topics.
He complained about mail-in ballots in the upcoming presidential election, lamented that there was “no retribution” by local authorities against acts of rioting, and litigated his past comments about American troops after assailing Pentagon leaders.
Repeating his past denials of The Atlantic’s report, Mr. Trump said only “an animal” would make the comments attributed to him. But he also reiterated his low opinion of John McCain, former prisoner of war and Republican senator who died in 2018.
“I was never a fan of John McCain,” the president said, accusing him of supporting “endless wars” and circulating “the fake dirty dossier” about Mr. Trump.
“Am I supposed to say, what a wonderful guy?” the president asked.