FAIRBORN — The Republican Party’s youth movement was on display Monday at Wright State University, as Florida’s Marco Rubio, the second-youngest U.S. senator, campaigned in support of Ohio Treasurer Josh Mandel, who now is running for Senate at age 34.

Rubio, 40, is considered by many to be the front-runner for the Republican vice presidential nomination. He has said repeatedly that he is not seeking the nomination, and reiterated that Monday night, saying he came to support Mandel’s campaign against U.S. Sen. Sherrod Brown, D-Ohio.

“You’re not just electing another senator; you may very well be electing the deciding vote over who the next majority leader is,” Rubio said, referring to party control of the Senate. “You want tax reform ... you want to repeal or replace ‘Obamacare’ ... you want to save Medicare and Social Security, you can’t do it with the people who are in there now. It does us no good to win the White House if Harry Reid is still in charge of the Senate.”

The Dayton area and Ohio have been at the heart of American politics in the past two weeks. Republican presidential candidates Mitt Romney and Rick Santorum visited the area just before the Super Tuesday primary won by Romney. Rubio made a nationally focused speech and gave his first endorsement of a Senate candidate to Mandel on Monday in Fairborn, and President Barack Obama and British Prime Minister David Cameron will be at an NCAA basketball tournament game today at UD Arena. Vice President Joe Biden will hold a rally in Toledo on Thursday.

Mandel and Rubio both mentioned the importance of Ohio on the national stage Monday. Mandel repeatedly told a standing-room-only crowd of more than 300 that Brown is “the most liberal senator in America,” and said Brown is “part and parcel” of a variety of changes the Obama administration has put in place.

“I wasn’t planning on running for United States Senate in 2012,” Mandel said. “But with my country being driven 100 mph at a brick wall by Barack Obama, Sherrod Brown, Nancy Pelosi and others, I decided this could not be the first time in my life that I said no to answering the call.”

Justin Barasky, spokesman for Brown, fired back at Mandel and Rubio, saying the “cut, cap and balance” budget pledge Mandel signed would “devastate” Social Security and Medicare, which are crucial to Ohioans.

“Look at who he’s aligning himself with — Rubio, who believes these programs have weakened us as a people,” Barasky said.

Barasky also said Brown is not always in lockstep with Obama.

“I think Senator Brown agrees with the president when he’s right, like when he invested in America’s auto industry,” Barasky said. “Josh would have voted against the auto industry rescue, (even though) 850,000 Ohioans work in that industry.”

The message from Mandel and Rubio appealed to the supportive crowd Monday at Wright State. Retired professor Mary McGirr of Washington Twp. said both men’s worries about an America in decline resonated with her.

“I have seven grandchildren, and I am worried that they will never have the freedoms that I have now,” McGirr said. “That’s what scares me. Not just the economy, but the liberties.”

While Rubio’s Ohio appearance comes as the state is in the national spotlight, he said that’s not a sign of him wanting the vice presidential nomination. He said he looks forward to helping any Republican president from the Senate.

Joel K. Goldstein, Saint Louis University law professor and vice presidential expert, said many eventual vice presidential nominees at first said they weren’t interested, pointing to George H.W. Bush in 1980, Dick Cheney in 2000 and John Edwards in 2004.

Goldstein said as the first Hispanic national party candidate, Rubio could help a candidate with Hispanic voters, as well as offer a boost in his crucial home state of Florida.

“Appearances across the nation may allow someone like Rubio to gain a national following or to score points with party leaders who will mention his name to the ultimate presidential nominee,” Goldstein said. “A vice presidential candidate can impact a close presidential race.”