Herman Cain is having one of the more improbable presidential campaigns in American history. Or at least of this cycle.

Once seen as a long-shot novelty act, the former pizza magnate is now getting the scrutiny of a front-runner, forcing him to tweak his 9-9-9 plan, reassure conservatives on abortion, and add staff. At least his fundraising has picked up, his campaign reports.

Speaking Friday morning in a run-down neighborhood in Detroit, Mr. Cain reacted to bipartisan criticism of his 9-9-9 plan – catchy for its simplicity – and made it a bit less simple. He would now allow some deductions, and set up “opportunity zones” to attract business investment in depressed neighborhoods. He suggested eliminating the minimum wage in struggling areas to boost employment.

At Tuesday’s debate in Las Vegas, 9-9-9 came under fierce attack from the other Republicans on stage, with data showing it would raise taxes for most Americans, in particular low-income people and the middle class. Cain’s original plan would eliminate all current taxes, including on capital gains, and replace them with a 9 percent tax on personal income, a 9 percent national sales tax, and a 9 percent business tax.

“When I look at this building behind me, I see opportunity – if we get capital gains out of the way,” Cain said after his speech in Detroit, according to the Associated Press.

“Because taxes and regulations have gotten so bad, people with money don’t want to take risks,” he added.

Cain also told reporters that the new elements he discussed on Friday were not a change. “We didn’t want to put it all out there at once,” he said.

The day before, Cain tried to put out the firestorm over views on abortion he had articulated Wednesday on CNN. He said he opposed abortion but added that “it’s not the government’s role or anybody else’s role to make that decision.”

“It ultimately gets down to a choice that that family or that mother has to make,” Cain said.

Again, Cain faced criticism. Former Pennsylvania Sen. Rick Santorum called Cain’s comment the “quintessential pro-choice position on abortion.”

On Thursday, Cain sought to clarify his views, issuing a statement indicating that he was merely addressing the role of a president on the matter. “The president has not constitutional authority to order any such action by anyone,” he said. “That was the point I was trying to convey.”

He also asserted that he is “100 percent pro-life” and would appoint judges who oppose abortion.

Cain’s abortion gaffe came just a day after he told CNN’s Wolf Blitzer that he would consider releasing all the prisoners from the US’s Guantánamo Bay camp in exchange for a US hostage. He later retracted that comment, saying he misunderstood the question.

Cain’s habit of misspeaking is a sign of his inexperience in politics. He has never held elective office and only ran for office once before, unsuccessfully. Suddenly, recent major polls show him, on average, in a statistical dead heat for the GOP presidential nomination with former Massachusetts Gov. Mitt Romney. Cain’s success in the business world, his charisma, and compelling life story as the son of working-class African Americans from Georgia have made him into the latest political sensation.

But with just over two months to go before the Iowa caucuses, it’s not clear Cain can hold up. He barely has a campaign infrastructure and has spent more time lately promoting his new book than slogging through Iowa, New Hampshire, and the other early nominating states.

In July, much of Cain’s Iowa staff resigned over his apparent lack of interest in competing in the early states. But on Thursday, Cain announced that Steve Grubbs, former chairman of the Iowa GOP, had joined the campaign as his Iowa chairman and strategist.

Cain is also getting outside help from a new "super political action committee," called Americans for Herman Cain and dubbed the “9-9-9 PAC.” In an e-mail Friday, organizer Jordan Gehrke wrote that in just 72 hours, the group has raised “well into six figures” and has more individual donors than super PACs for Mr. Romney and Texas Gov. Rick Perry combined.