Novi, Michigan CNN  — 

Gov. Scott Walker on Monday sought to use President Barack Obama’s slipping popularity on foreign policy issues as a punching bag and sought to bolster his own credentials ahead of a likely presidential bid.

Speaking in Novi, Michigan, the Wisconsin Republican rallied around the plight of a Michigan man who has been held hostage in Iran since 2011 and blasted Obama for failing to do enough on the missing man’s behalf – as well as failing to ward off attacks by Islamic terrorists around the world.

Speaking at an Oakland County Republican Dinner, Walker listed terrorist acts committed by individuals affiliated with ISIS and others who sympathize with the group.

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“That’s something that worries you not just about places elsewhere around the world; you suddenly start to realize it’s happened in France, in Belgium, in Canada. Lord knows what happened in the last day or so down in Texas and elsewhere around the country,” he added. “You start to realize this isn’t something we can just leave to page seven in the newspaper.”

Walker also tied Democratic frontrunner Hillary Clinton, who served as Obama’s secretary of state for four years, to the president.

“If you think about the last six years, of which the first four, Hillary Rodham Clinton was the person who advised the President on issues around the world, if you think about where this president is at today and where we stand in the world today, I gotta tell you, that disturbs me about as much as anything we’ve talked about tonight,” Walker said.

More than ever, he said, the country “needs a commander-in-chief to stand up and identify that radical Islamic terrorism is a threat to us all.”

Walker, who has yet to formally declare his candidacy, has been raising money and touring the country ahead of his likely bid. At times, he’s stumbled when addressing foreign policy issues. In particular, he was criticized for comparing pro-union protestors gathered in Madison, Wisconsin, to ISIS fighters.

Potential rival, Florida Sen. Marco Rubio, also took a shot at Walker – and other governors seeking the presidency – during a recent interview with the Des Moines Register editorial board.

“Governors can certainly read about foreign policy, and take briefings and meet with experts, but there is no way they’ll be ready on Day One to manage U.S. foreign policy,” said Rubio, who serves on the Senate Foreign Relations Committee and has sought to carve out foreign policy as a strength.

Walker’s response to Rubio: “I think he’s questioning how Ronald Reagan was ready.”

The Wisconsin governor met Monday in Flint, Michigan, with the family of Amir Hekmati, a former Marine who’s been held hostage in Iran since 2011, and criticized Obama for not doing enough to help.

“The President of the United States hasn’t even spoken his word – the word of his name publicly, while he’s talked about others who are being held,” Walker said.

ABC News reported that Hekmati was taunted by Iranain prison guards when Obama called for the release of an American journalist–Jason Rezaian – at the White House Correspondents’ Dinner last month but didn’t mention Hekmati.

Vice President Joe Biden visited Hekmati’s family in Michigan on Sunday, and a sister of Hekmati told Fox News that her family “felt very optimistic” after the visit.

“He really reassured us from the highest levels this is a very, very important topic of conversation,” she said.

Biden also tweeted Monday, calling for Hekmati’s release.