Jeb Bush, shown here with George W. Bush in 2006, has alarmed some supporters and energized opponents by handling questions about his support for his brother and the Iraq war less than deftly. (Alex Wong/Getty Images)

— Jeb Bush came face-to-face here Wednesday with the perils of carrying a politically divisive family name, skirmishing with voters over the Iraq war and continuing to struggle with how to differentiate himself from his brother.

Asked repeatedly in recent days whether he would have supported an Iraq invasion based on what is known now, the former Florida governor has replied “Yes” or “I don’t know,” or has refused to answer, depending on the venue.

The stumbles mark the toughest period yet for Bush’s still-undeclared campaign and have lit a fire under his likely GOP opponents, many of whom have happily proclaimed that they would not have authorized the Iraq invasion under those conditions. Many conservative leaders and pundits are also lacerating Bush as appearing unprepared to address an obvious topic and are casting him as a tone-deaf relic of the GOP elite.

“These are the questions that are extraordinarily important for the country, and I think if you’re considering running for president you need to answer the question,” New Jersey Gov. Chris Christie (R), who is weighing his own 2016 bid, said on a radio program Wednesday.

The debate within the GOP over a 12-year-old invasion reflects the extent to which Iraq has become the Republican Party’s Vietnam — a factious and largely failed undertaking that the party once supported but would now like to forget. The “Would you have authorized the war?” question allows even the most hawkish Republicans to answer “No,” given that U.S. forces never discovered the weapons of mass destruction that were the basis for the military operation.

George H.W. Bush with sons George W. and Jeb boating in Kennebunkport, Maine, in 1989. (George Bush Presidential Library)

The dispute also highlights Bush’s vulnerabilities as he moves closer to formally launching a campaign, including his lack of familiarity with the digital pace of modern politics and his difficulties in clearly defining himself apart from his family name.

That name helped Bush become one of the immediate front-runners in the GOP race, trouncing most of his would-be opponents in fundraising and building a massive network of advisers with loyalty to his family. He has consistently declared that he is his “own man,” but he has also taken pains to praise his brother, former president George W. Bush, and father, former president George H.W. Bush.

Jeb Bush was asked by reporters several times Wednesday how he was different from the other two Bushes. He started off with a joke: “I’m much better looking than my brother. I’m much younger.”

When pressed again, Bush did not cite specific differences but said he is running in a different political environment. “Of course I have differences with every previous president,” he said, without offering any.

Earlier Wednesday, at the end of a rowdy town-hall meeting in Reno, Bush had a testy exchange with a 19-year-old Democratic college student who said, “Your brother created ISIS,” referring to the Islamic State terrorist group.

Then the student, Ivy Ziedrich, complained that Bush was being “pedantic” in response to her remarks.

Former Florida governor Jeb Bush (R) is taking heat for a series of answers he gave on whether he would have authorized the war in Iraq. Here’s what he said this week. (Jhaan Elker/The Washington Post)

“Pedantic? Wow,” Bush said curtly, before arguing that President Obama is partially responsible for the outbreak of violence in the region.

“You can rewrite history all you want, but the simple fact is that we’re in a much more unstable place because America pulled back,” Bush said.

‘George Bush 3’?

In addition to Christie, at least five other potential Bush rivals have said in recent days that they would not have backed the invasion if they knew in 2003 that the intelligence on Iraqi weapons was inaccurate: Sens. Ted Cruz (Tex.), Rand Paul (Ky.) and Marco Rubio (Fla.), plus Ohio Gov. John Kasich.

“To say that nothing would happen differently means we’re going to get George Bush 3,” said Paul, who is attempting to bridge the hawkish and libertarian wings of the GOP.

Rubio had said as recently as March that the Iraq war was a good idea because “the world is a better place without Saddam Hussein.”

But on Wednesday he had an alternate take and roped in Bush’s brother at the same time. “Not only would I not have been in favor of it, but President Bush would not have,” Rubio told reporters after delivering a speech on his “Rubio Doctrine” in New York.

The leading contender on the Democratic side, former secretary of state Hillary Rodham Clinton, has stayed out of the fray entirely, perhaps in part because she has her own difficulties explaining her 2003 vote for the Iraq war.

For Bush, his handling of questions about Iraq and his family has prompted broad criticism from conservative observers.

“I don’t get it. How could you not have been ready for this question?” said conservative activist Grover Norquist, who has clashed with Bush over taxes. “The answer was odd, but the lack of preparation was odd and unusual.”

GOP hawks are also alarmed by Bush’s muddled responses and wonder whether he will be able to make a full-throated case for the interventionist foreign policy they favor.

Former diplomat John Bolton — who may announce his own 2016 Republican bid Thursday — said Bush could have pushed back harder on his interviewers and sounded more coherent about one of the most controversial foreign policy decisions of recent decades.

“The questions have been as sharply analytic as a bowl of oatmeal. It’s like asking, ‘Would you support the Crimean War, yes or no?’ ” he said. “My answer would have been: ‘If you knew everything you do today, of course you’d make different choices, but I’d still overthrow Saddam Hussein, who was a threat to peace and stability in the region.’ ”

James Mann, who has written two books about George W. Bush’s foreign policy team, said the issue allows the GOP field to isolate Jeb Bush.

“It’s a way to let Bush be out front on an issue where he’s uncomfortable,” Mann said. “They get to treat the war as history and let Jeb be the only one who has to squirm on the details of it.”

Late-night fodder

Bush’s slips have bubbled up from the Beltway sphere into popular culture. On Comedy Central’s “The Daily Show,” Jon Stewart mocked him by saying, “I think most of America agrees that when it comes to foreign policy, George W. Bush is an excellent painter.” David Letterman, in his monologue for CBS’s “Late Show,” called Jeb Bush an imitation of his brother: “If George W. Bush is Marvin Gaye, Jeb Bush is Robin Thicke.”

The heavy focus on Jeb Bush’s family problems began last week after reports that Bush told donors that his brother was one of his top advisers on Israel policies.

The conservative advocacy group ForAmerica released an online advertisement this week calling Bush “unelectable.” The group’s president, L. Brent Bozell, and other figures on the right say they are attempting to formulate a plan for toppling Bush, possibly by rallying behind one of his opponents.

“If Jeb Bush is nominated, Hillary Clinton is elected. There is no doubt in my mind about that,” Bozell said in an interview Wednesday. “Republicans can’t win without a conservative base that is inspired.”

Aides defended Bush, saying that he has been asked questions about the Iraq war many times this year without incident.

After a foreign policy speech in Chicago in February, Bush told the crowd, “There were mistakes in Iraq for sure.” But he also defended the 2007 troop surge as “one of the most heroic acts of courage politically that any president’s done, because there was no support for this.”

This week’s struggles have not prompted any reconsideration of Bush’s long-term campaign strategy, aides said. That includes directly interacting with voters in town-hall-style meetings as he did Wednesday in Reno.

“I’ve been asked hundreds of questions both from the press and people,” he told the audience at a community center. “This isn’t scripted. As they say back home, you can let the big dog eat.”

Costa reported from Washington. Karen Tumulty contributed to this report.