U.S. House Speaker Paul Ryan, of Janesville, endorsed Trump earlier this month, but has since decried remarks the candidate made about a Latino judge as the "textbook definition of a racist comment." And this week, Ryan emphasized his opposition to Trump's call for a temporary ban on Muslims coming to the U.S. saying that wasn't "in our country's interest" or "reflective of our principles not just as a party, but as a country."

Republican Sen. Ron Johnson, who is in a tough re-election fight with Democrat Russ Feingold, has said he supports Trump but doesn't endorse him. Johnson this week also said he disagreed with Trump's proposed ban on Muslims.

Walker previously said he would endorse Trump as the GOP nominee, but last week hedged by saying he wanted to see how Trump conducted himself between now and the national convention next month in Cleveland.

Trovato has spent years behind the scenes in Republican politics. When he was a student at the UW-Madison, Trovato worked as an intern for Walker, who was in the state Assembly at the time. According to an online biography, Trovato also served on the executive board of the Waukesha County Republican Party and the Republican Assembly Campaign Committee, and worked as a policy adviser for the Wisconsin State Assembly.