When Jeb Bush was serving as governor of Florida, eight hurricanes and four tropical storms crashed into the coasts of that state in less than a year and half, leaving more than $100 billion in losses in their wake.

As a pediatric neurosurgeon in 1987, Ben Carson separated two twins who were conjoined at the head — a medical first and not his only such accomplishment.

But in the race to become next year’s Republican presidential nominee, Wisconsin Gov. Scott Walker says he has faced down greater tests in public service than either of these men or any of their other GOP rivals.

“With all of the challenges that we face around the globe today, now is not the time for untested leadership. I have been tested like no other candidate in this race,” Walker said in a foreign policy speech last month in South Carolina.

As the veteran of massive labor protests and the only governor in American history to survive a recall election, Walker says he has what it takes to eradicate terrorists like the Islamic State group and reshape Washington, D.C., into a new and more conservative form. But his 2016 rivals — Walker himself has called them the strongest Republican field since 1980 — can make compelling cases of their own.

At the moment, Walker is trailing in the polls to candidates such as Carson and reality television star Donald Trump, men who have never held public office. Julian Zelizer, a political historian at Princeton University, said that being tested is nothing new for a presidential contender.

“This is a common thing for candidates to say in this age of cutthroat politics, an effort to show they can withstand challenges once in office and equally important during the general election campaign. But the term is used so much it’s not clear how much traction that will give (Walker) as he tries to come back from a summer of being drowned out by Trump,” said Zelizer, whose books include a biography of President Jimmy Carter and an examination of the politics of national security.

Here’s just some of the challenges that other candidates have undergone:

  • Bush and New Jersey Gov. Chris Christie led their respective states during separate devastating hurricanes, including the eight hurricanes that hit Florida in 2004 and 2005, according to the Miami Herald.
  • Carson, who is African-American, was raised in Detroit by a single mother and went on to become the director of pediatric neurosurgery at Johns Hopkins Children's Center. He broke new ground in medicine for his patients and also worked on cases in which patients died, as in the unsuccessful 2003 surgery involving two Iranian twins joined at the head. "I'm the only one to separate Siamese twins," Carson said in a breakout moment in the first GOP presidential debate. "The only one to operate on babies while they were still in the mother's womb, the only one to take out half of a brain _ although you would think if you go to Washington someone had beaten me to it."
  • George Pataki, a long-shot candidate for the Republican nomination, served as the governor of New York on Sept. 11, 2001, and in the aftermath of that day's terrorist attacks.

David Maraniss, a journalist and Madison native who has written biographies of both Bill Clinton and President Barack Obama, said Walker’s labor battles could also be seen as a “one-hit wonder.”

“It is a stretch for him to say he has been tested more than Hillary Clinton, (Vice President) Joe Biden, Jeb Bush, (Ohio Gov.) John Kasich, and even Chris Christie,” Maraniss said.

As Walker lays out the case for himself and for a more aggressive American policy at home and abroad, he has pointed to his record of holding firm on his plan to repeal most collective bargaining for most public employees in the face of tens of thousands of demonstrators.

He has pointed to the fact that as governor he has presided over a conservative reordering of Wisconsin politics that has encompassed everything from allowing the concealed carry of handguns to putting new rules on abortion providers.

That approach has often worked for the governor, particularly in the spring and early summer of this year. Walker could tout his recall success and the 2011 protests that were as big as any that Madison had seen since the era of the Vietnam War.

“Republicans want a fighter — an aggressive candidate who speaks in declarative sentences and without apology, not a candidate who imagines that Republicans can avoid a fight. For now Walker is giving them the combatant they want,” Jennifer Rubin, a conservative commentator for The Washington Post, wrote in March.

But it has also flopped, as it did when Walker told activists at the Conservative Political Action Conference that standing up to protesters showed he could face down terrorists as well. At the moment, Trump is the one wooing Republicans with tough talk.

James D. Boys, a professor at Richmond University in London and specialist on American foreign policy, said that so far Walker’s emphasis on having been tested has served to emphasize the governor’s lack of national security credentials. Boys has written a book on Bill Clinton’s foreign policy and a forthcoming book on Hillary Clinton and her rise to Democratic front-runner status in the current presidential race.

Walker has failed so far to follow the path of other former governors like Bill Clinton and Ronald Reagan who successfully built up their credibility on foreign policy while seeking the White House, he said.

“What is problematic about Scott Walker to date, however, is his continuing propensity to rely on platitudes for answers and his failure to use the road to the White House as a training ground for power, as other successful candidates have done in the past,” Boys said.