By Nick Carey

MADISON, Wisconsin (Reuters) - Over the past year Wisconsin's Republican governor, Scott Walker, has worked his way down a checklist of items commonly associated with a run at the U.S. presidency.

He has written a campaign-themed book and visited Iowa, New Hampshire and other pivotal election-year states. He has stumped for candidates nationwide. He even has criticized conservatives who challenge moderate incumbents, pleasing party elders.

With a growing pre-presidential checklist, it is little wonder Walker is beginning to emerge as a top-tier candidate in a potentially crowded field in 2016. But first, he must win a tough reelection race in 2014, against Democratic businesswoman Mary Burke, his only announced opponent.

"Walker is working his way down the presidential to-do list," said Mordecai Lee, a political science professor at the University of Wisconsin in Milwaukee. "He's doing the formula to a 'T'."

He is hardly alone. Besides Christie, other Republican White House aspirants include two U.S. Senators, Rand Paul of Kentucky and Marco Rubio of Florida. Others are expected to join in, possibly including Ted Cruz, the Texas tea party favorite, or another governor, such as Rick Perry, also of Texas. None of them have officially declared their candidacy as yet.

Still, a Walker run would face big hurdles. He is little known outside conservative circles and is seen as lacking charisma. He has not shown an ability to raise the funds needed to compete against Christie or another widely backed opponent.

If Walker made it to the general election, Republican strategists say, Democrats would hammer him on his record, including his backing of a 2011 bill that curtailed collective bargaining rights of public-sector workers and support for a 2013 law requiring women seeking abortions to first have an ultrasound.

Despite those weaknesses, University of Virginia political scientist Larry Sabato has Walker as the top potential 2016 GOP contender in his closely followed Crystal Ball website.

Story continues

"Walker has a lot to prove, but he looks good on paper," said Crystal Ball managing editor Kyle Kondik. "There are a lot of questions about how he will perform as a national candidate."

TOUGH RACE

None of the conjecture will matter unless Walker first beats Burke in Wisconsin's 2014 gubernatorial contest. A Marquette University Law School poll of registered voters last October showed the candidates in a virtual dead heat, with 47 percent of respondents favoring Walker and 45 percent for Burke. But Burke may have room to build support, with 70 percent of those polled stating they do not yet have an opinion about her.

Walker, by contrast, is polarizing. Fifty percent of those polled view him favorably, 47 percent unfavorably, and only 4 percent have neither a favorable or unfavorable view of him.

Walker is best known nationally for turning back a recall vote in 2012 after his battle with the state employee unions. His surprisingly strong 53 percent to 46 percent margin against a well-organized union effort won him followers among conservatives nationwide.

The recall campaign also helped Walker build a national fundraising apparatus that could prove helpful in the 2014 election and beyond. He raised $37 million to defeat the recall, a substantial figure for a Wisconsin candidate, and as of last June had $2.26 million cash on hand for his campaign. The figure will be updated on January 31.

For Wisconsin voters who know him well, Walker's governance record is mixed. Walker has earned a reputation as a fiscal hawk, posting a $911 million budget surplus last year after inheriting a budget deficit upon taking office three years ago. And he aims to funnel most of the surplus to residents through tax breaks he dubs a Blueprint for Prosperity.

"Our reforms are helping the people of Wisconsin create more jobs and more opportunity," the governor said in his January 22 State of the State speech.

But the progress on jobs is far short of what Walker promised during his 2010 election campaign. Walker said he would create 250,000 jobs in his first term, but government data show only around 40,000 more people have jobs today than when he took office. Wisconsin ranked 37th among the U.S. states in private-sector job creation in the year ending June 2013, the last period for which data are available.

Burke is expected to challenge Walker on the jobs issue. A former Trek Bicycle executive, and daughter of the company's founder, Burke has a business background that could appeal to moderate Republicans and an emphasis on education and women's access to healthcare that should play well with Democrats.

Burke also is positioning herself as a salve to the tempestuous Walker years. "Wisconsinites don't appreciate the divisiveness of the governor," she told Reuters in an interview.

In many respects, the campaign could shape up as a referendum on Scott Walker.

"We're seeing incredible grassroots support for getting rid of Scott Walker," said Lisa Subeck, executive director of United Wisconsin, a liberal group that worked to recall Walker in 2012. United Wisconsin's website features a "Scott-Free 2014" fundraising button on its home page.

John Binder, an independent voter in central Wisconsin, is no fan of unions but says Walker has been too aggressive.

"We're not used to scorched-earth politics around here," he said. "I'm not sure I want four more years of Walker."

To win, Walker will need to mobilize conservatives who rallied around him in 2010 and again during the recall vote.

Some conservatives may be disappointed Walker did not fight harder against federally imposed education standards, said Matt Batzel, state director for American Majority Action, which provides training for local activists.

"But conservatives will rally around Walker when the left-wing attacks begin," Batzel said.

The University of Wisconsin's Lee said the few voters with no opinion on Walker will be key to victory in November .

"Walker is the presumptive frontrunner," Lee said. "But it will by no means be a slam dunk."

"UNINTIMIDATED"

If Walker does win re-election in November, he would need to quickly change gears and make his way into a national contest dominated so far by Christie.

Walker has indicated he is eyeing a White House run. The book he published after the recall vote - "Unintimidated: A Governor's Story and a Nation's Challenge" - sought to position him on the national stage. And when the Washington Post inquired about his ambitions at a March 2013 conservative conference, he allowed that some day "we'll take a look at" a White House bid.

Walker and Christie have one point in common: They both are Republican governors in states where Barack Obama won in 2012. But with that, their similarities end.

Christie is moderate, charismatic and a powerful national fundraiser. Walker lacks Christie's pugnacious style, and though he raised money nationally in defeating the recall, he has not proven he could do so for a national campaign.

Still, those who believe in Walker's prospects say the recall trial is what gave him a shot at a presidential bid. In defeating Milwaukee Mayor Tom Barrett in the recall, Walker showed he can turn back a national Democratic effort to defeat him, according to the Crystal Ball's Kondik.

"In many ways Walker is a Democratic creation," Kondik said. "Without all the Democratic opposition to him, he wouldn't have the same appeal."

The University of Wisconsin's Lee said a key Walker strength is his discipline in sticking with an economic message. He has signed socially conservative legislation, but on the stump avoids social issues that can trip up conservatives during general-election races.

"Scott Walker can stay on message all day," Lee said. He "is the closest thing out there to the Tea Party's dream candidate, but can present himself in a way that doesn't make him seem like a Tea Party person."

Republican strategist Ford O'Connell says Walker will need to hone his campaigning skills. But his conservative credentials make him the "GOP dark horse candidate in 2016."

(Editing by David Greising and David Gregorio)