And somehow, Mr. Trump made the day’s news about his own problems with the news media. He called on journalists “to set a civil tone” and to “stop the endless hostility and constant negative and often false attacks and stories.”

Then Mr. Trump again directed the crowd’s attention to his bipartisan efforts: “By the way, do you see how nice I’m behaving tonight?” he asked. “Have you ever seen this? We’re all behaving very well!”

(Minutes later, the president broached the topic yet again: “I think we will be bipartisan on infrastructure.”)

Still, the performance by Mr. Trump and the slate of Wisconsin Republicans who took the stage here served as further confirmation that, with less than two weeks to go until a round of midterm elections in which the leadership of the House is at stake, not even reports of explosive devices could do much to halt months of highly divisive messaging at campaign rallies.

Mr. Trump did address the reports in his opening remarks, calling the episodes “an attack on our democracy itself” and promising swift justice.

“Such conduct must be fiercely opposed and firmly prosecuted,” the president said. “We want all sides to come together in peace and harmony. We can do it.”

Two other Republicans who took the stage here at an airport hangar in the 4,000-person town of Mosinee began their speeches with a short disclaimer — essentially, terrorism is bad — before denouncing Democrats for their immigration policies and the cost of health care.