“The more he started to talk, the more I became repulsed by what he was turning the Republican Party into,” Mr. Sama said.

Since then, he has shifted. He likes the deregulation, the tax cut and the fact that Mr. Trump has not started a war. He is still apprehensive about Mr. Trump, but he has decided to vote for him for these policies — and as a way to stop the Democratic Party.

“I was like, ‘Come on, this is ridiculous, he’s not smart enough to be able to collude with another country!’” he said. “The Democrats have gone so far from reality, and they are coming across as so unreasonable, that it makes it look like they are out to get him.”

Wisconsin’s suburbs have grown less white and more educated, but the change has been slow and, at least so far, less important for its politics than a stark and relatively sudden political shift among white men without a college degree, said Charles Franklin, director of the Marquette Law School Poll. In 2012, when he started polling, those men were about 5 points more likely to identify as Republican than Democrat. Now they are 18 points more likely to call themselves Republican, while other more educated groups have not changed much. That has erased the slight advantage Democrats used to enjoy in the state, Mr. Franklin said, making it a dead heat.

Charlie Sykes, a former editor of RightWisconsin who broke with the Republican Party over Mr. Trump, said the question was not whether Mr. Trump would win in Waukesha County, but by how much. Margins are incredibly close, and if Republican moderates fail to support Mr. Trump here or in Milwaukee County, where he received his second highest vote tally among Wisconsin counties in 2016, he might not have enough to counter Democrats in urban areas.

The Democratic nominee is important, too. If it is Bernie Sanders, “they’d be saying, ‘Yes, Donald Trump is toxic, but I’m sorry, we are out of this if you are going full socialism,’” Mr. Sykes said.

In a sign the parties are fighting over every vote, the Milwaukee County Republican Party announced Thursday it was opening a field office in downtown Milwaukee, deep in Democratic territory.