Wisconsin is a doubly important state for both parties. Its 10 electoral votes are critical in the presidential election, and the last time a Republican won there was 1984.
Priebus said that Wisconsin is the competitive race where the GOP is strongest in its battle to win control of the upper chamber.
"I think if there's any seat right now that we're the strongest in, in America, as far as a challenge race, it's Wisconsin. I mean Tommy Thompson is the absolute perfect candidate to win that seat," he said.
And he said there were no concerns that the competitive primary — where four candidates battled it out in a tough race for the Republican nomination — would boost Democratic nominee Rep. Tammy BaldwinTammy BaldwinOvernight Finance: Wall Street awaits Brexit result | Clinton touts biz support | New threat to Puerto Rico bill? | Dodd, Frank hit back Dem hopeful that Congress will eliminate tax break for investment fund managers Congress should stop government hacking and protect the Fourth Amendment MORE.
"I'm one of these guys that big, tough, primaries are good. I like it. It makes a candidate stronger."
Preibus, a Wisconsin native, also praised his longtime friend, GOP vice presidential candidate Paul RyanPaul RyanHouse to vote on NRA-backed gun measure Congress fails on promises to restore regular order and stop funding by crisis The only common ground between Donald Trump and Paul Ryan is an "R" MORE, who polls show has boosted Romney's chances in the state.
"He tries to win the mission every day. He works hard. He waits on God's timing and really good things happen. I would say Paul is one of these win-the-day guys — set goals and meet goals," he said.
Preibus also expressed confidence Paul would give a great speech at the convention. "There's no doubt that Paul will hit it out of the park on Wednesday."