Wisconsin Gov. Scott Walker makes a campaign stop at Kroll's West in Ashwaubenon, Wis., on Election Day, Tuesday, Nov. 4, 2014. (AP Photo/The Green Bay Press-Gazette, H. Marc Larson) NO SALES Mary Burke, Democratic gubernatorial candidate, makes a campaign stop at the Democratic Party of Brown County headquarters in Green Bay, Wis., on Election Day, Tuesday, Nov. 4, 2014. (AP) - His presidential aspirations on the line, Republican Scott Walker asked voters in Wisconsin on Tuesday to send him to the governor's mansion for the third time in four years. A victory over Democratic businesswoman Mary Burke could push Walker to the top tier of potential 2016 candidates, while a loss would almost certainly dash his White House ambitions. His race was one of three dozen contested Tuesday in the nation's midterm elections. Walker gained a national profile shortly after taking office in 2011, as he pushed lawmakers in Wisconsin to take away the collective bargaining rights of most state workers. Opponents responded by trying to boot Walker from office, and he became the first governor in U.S. history to survive a recall election the following year. While Walker has downplayed talk of a White House bid during his re-election effort, his conservative agenda would likely form the backbone of an eventual campaign. Walker argued this year he deserves a second term after working with the GOP-controlled Legislature to wipe out a $3.6 billion budget shortfall and cut taxes by $2 billion, and presiding over the addition of more than 110,000 private-sector jobs. Burke told voters Wisconsin could have done better, blasting Walker for falling far short of his promise to add 250,000 new private-sector jobs during his first term. She notes next year's budget in Wisconsin includes a $1.8 billion shortfall. The economy also looms large for two other Midwestern governors. In Ohio, Republican Gov. John Kasich is cruising to a second term in a key battleground state, largely on a record of economic growth and shrinking unemployment. In Michigan, GOP Gov. Rick Snyder is in a tight race with Democratic challenger Mark Schauer. The incumbent has struggled to translate his state's improving economy into political dividends. Both states are among a handful of important presidential battlegrounds, including Colorado and Florida, where governors are on the ballot Tuesday. A look at some of the most competitive contests in the country: Republican Gov. Rick Scott is in a tight race with Democrat Charlie Crist in the nation's largest swing state. The campaign is among the most expensive and nasty in the country, with both sides and their allies spending more than $100 million on television ads. Florida Democrats are hoping that Crist, a former Republican governor, can leverage his statewide recognition to help notch the party's first gubernatorial win in 20 years. Republican Gov. Sam Brownback is struggling in his first bid for re-election after putting in place the most conservative agenda of any governor in the country. His prescription of massive tax and spending cuts generated a public backlash, and many Republicans have defected from him and now support Democrat Paul Davis, the state House minority leader. Democrat Martha Coakley seeks to become the first woman elected governor in Massachusetts history, while Republican Charlie Baker is trying to return the office to GOP hands for the first time since Mitt Romney left in 2007. Coakley, the state's attorney general, is looking for political redemption after suffering an upset loss to Republican Scott Brown in the 2010 special election to succeed the late Sen. Edward Kennedy. She led Baker in polling early in the race for governor, but recent surveys have shown the Republican pulling slightly ahead. Democratic Gov. Pat Quinn faces a tough challenge from wealthy GOP businessman and first-time candidate Bruce Rauner. Republicans see Tuesday as a chance to reclaim the governor's office for the first time in more than a decade. Democrats are worried about a less-than-enthusiastic electorate in a midterm race, keenly aware that Quinn won narrowly in 2010 - by just 32,000 votes out of 3.7 million cast. Rauner has poured $26 million of his fortune into the race, criticizing the incumbent Quinn as a "failure." Quinn has pushed to raise the minimum wage while blasting Rauner as an out-of-touch "billionaire." Democrat Mike Michaud would be the nation's first openly gay governor if he can unseat GOP Gov. Paul LePage, the only Republican governor now serving in New England. LePage squeaked into office in 2010 with 38 percent of the vote in a three-way race, and his inflammatory rhetoric and partisan agenda have made him a divisive figure. While polls suggest the race is a tossup, Michaud got a boost last week when independent candidate Eliott Cutler scaled back some advertising and said anyone who doesn't believe he can win should vote for someone else. Democrat Tom Wolf appears poised to send Republican Gov. Tom Corbett to a historic defeat, making him the first incumbent to lose in the four decades since Pennsylvania's chief executive was allowed to seek re-election. Gov. Nathan Deal, a Republican, faces a challenge from Democrat Jason Carter, a state senator and the grandson of former President Jimmy Carter. Follow Michael J. Mishak on Twitter at https://twitter.com/mjmishak