LA CROSSE, Wis. — President Obama came to this city on the Mississippi on Thursday and launched a frontal assault on Gov. Scott Walker of Wisconsin, who filed papers earlier in the day that moved him closer to joining a crowded Republican presidential field.

Mr. Obama likened Mr. Walker and the “bus full” of Republican candidates to an “Uncle Harry” at Thanksgiving dinner who says something that makes no sense.

“You still love him,” the president said. “He’s still a member of your family. Right? But you’ve got to correct him. You don’t want to put him in charge of stuff.”

Mr. Obama compared the recent economic performance of Wisconsin under Mr. Walker with that of its neighbor Minnesota, where Democrats have been in charge. He pointed out that Minnesota had raised taxes on the wealthy, increased the minimum wage and expanded its Medicaid program to offer health insurance to more of the needy — none of which has happened in Wisconsin. Minnesota’s unemployment rate is lower, he said, and its median income is higher.