MADISON, WI — The presidential ambitions of Wisconsin’s conservative governor were on the line Tuesday in one of several hard-fought gubernatorial races across the U.S. that could resonate in the 2016 White House election.

Also closely watched was Florida’s toss-up race between Republican Gov. Rick Scott and challenger Charlie Crist, a former Republican governor-turned-Democrat who is hoping his statewide recognition will give the Democratic Party its first gubernatorial win there in 20 years. That would put Florida, a crucial battleground state with its large population of senior citizens and Hispanics, in friendly territory for the Democrats in 2016.

Governors were on the ballot in 36 states Tuesday, most of them overshadowed by the fierce fight for control of the Senate, where Republicans need just six seats to take over. But several close governors’ races have drawn campaign appearances from potential White House contenders, including Hillary Rodham Clinton and New Jersey Gov. Chris Christie, as they try to raise their own profiles and cement alliances for 2016.

In Wisconsin, a victory over Democratic businesswoman Mary Burke could push Gov. Scott Walker to the top tier of prospective 2016 candidates, while a loss would almost certainly dash his White House aspirations.

Walker became a conservative favorite and 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.

Another governor who has figured in the 2016 discussion, John Kasich of Ohio, was cruising to a second term largely on a record of economic growth and shrinking unemployment. Kasich’s state is also major presidential battleground, its voters neither reliably Republican nor Democrat.

In another swing state, Colorado’s Democratic governor was in a tight race with a Republican challenger. Republicans also see a chance to reclaim the governor’s office in Illinois — the adopted home state of President Barack Obama — for the first time in more than a decade.

Republican governors, meanwhile, were facing tough re-election battles in Kansas, Michigan, Pennsylvania and Maine.

___

Associated Press writers Scott Bauer and Michael J. Mishak contributed to this report.

___

Follow Michael J. Mishak on Twitter at https://twitter.com/mjmishak