Ryan has long looked up to Thompson, calling him "Wisconsin's greatest governor" in 2004.

"On a personal note, Tommy has been my greatest mentor. Of all things, he taught me that public service is about helping people reach their potential," Ryan said at the time. "He is a man of passion, big ideas and boundless enthusiasm."

The two are likely to stump together when Ryan is in the state.

The new VP candidate might have already helped Thompson, who won his Tuesday primary. While all four GOP Senate hopefuls were at a homecoming rally last Sunday for Ryan and Romney, Thompson was the only one Ryan name-checked, possibly giving him the boost he needed to beat businessman Eric Hovde (R) in the hard-fought race. He'll face Rep. Tammy BaldwinTammy Suzanne BaldwinDem senators unveil expanded public option for health insurance Dem senators call on FCC to protect against robocalls GOP Senate hopefuls race to catch up with Dems MORE (D-Wis.) in the fall.

"We see a president who took what we pioneered here in Wisconsin, Tommy Thompson, welfare reform, getting people off of welfare and back to working and lives of dignity and personal responsibility, on to a life of hitting their potential," Ryan said while attacking President Obama.

Thompson jumped on the comment, using it in a last-minute campaign ad and sending campaign emails touting a Ryan-Romney-Thompson ticket.