WASHINGTON -- On Monday, Herman Cain ventures inside the Beltway, where his presidential campaign is viewed as intriguing, a bit baffling and not quite serious.

Cain is conducting a policy forum at the American Enterprise Institute, a conservative think tank. That's followed by an appearance at the National Press Club, courting the Washington elites whom most candidates spend considerable time campaigning against yet rely on for strategy, fundraising and exposure. He also is meeting with the Georgia members of Congress.

As the Stockbridge resident has risen to the top of the polls, Republican political veterans and opinion leaders have been picking apart his 9-9-9 tax plan, lack of foreign policy knowledge and campaign trail gaffes. In recent weeks, Cain has half-apologized for saying that the U.S. should build an electrified fence on the Mexican border and for saying in a television interview that abortion, under some circumstances, is a "choice" -- a view rejected by the conservative GOP base.

Some in D.C. envision a steep fall in the polls to accompany Cain’s quick rise, as was the case for Rep. Michele Bachmann of Minnesota and Gov. Rick Perry of Texas.

“I don’t think Cain has lasting strength,” said Tony Fratto, a Republican strategist and former spokesman in the George W. Bush White House.

“I do think it’s a bit of a novelty. ... Some of it’s being exposed a little bit," Fratto said. "The foreign policy hole is huge. You could drive a truck through it. When he says, ‘I will study hard and hire smart people,’ that’s not the answer for the commander in chief.”

In a recent appearance on Fox News, conservative columnist Charles Krauthammer was blunt in addressing Cain’s adjustments to the 9-9-9 plan and his stumbles on abortion.

“It’s not just he hasn’t thought it out -- he’s winging it,” Krauthammer said, “and that’s a real problem.”

Cain spokesman J.D. Gordon said the campaign is working on foreign policy strategy with former ambassadors and Pentagon officials, and said this week's congressional outreach is key.

"As the president, you’re going to have to be working with Congress. That’s why it’s important," Gordon said. "Mr. Cain has become friends with a number of members of the Georgia congressional delegation, and so they have been very welcoming."

Still, as Cain prepares to meet with the state's eight GOP House members at their weekly meeting, four have endorsed former Rep. Newt Gingrich of Georgia while the rest have not publicly backed a candidate. Cain has yet to earn a congressional endorsement.

The rise of the former Godfather's Pizza CEO and radio host on AM 750 and 95.5 FM News/Talk WSB was driven, in part, by his revolutionary and simple tax plan: a 9 percent income tax, 9 percent corporate tax and 9 percent national sales tax. There are a few exceptions, such as a tax exemption for charitable donations, zero income tax for the poor and carve-outs for economically depressed “empowerment zones.”

The plan has been attacked for shifting more of the tax burden to the middle and lower classes and for drastically reducing revenue. For conservatives, the primary concern is the national sales tax. Cain’s foes took aim at the sales tax during recent debates, and conservatives argue that the sales tax could increase from 9 percent and could grow into a “value added tax,” which is applied at every sale along a supply chain.

“What we know from European taxes is they don’t come and go away, they don’t come and stay at the rate they come in on, they come and grow,” said Grover Norquist, the president of anti-tax group Americans for Tax Reform and a highly influential conservative.

He added that Cain’s ultimate goal of only having a national sales tax, known as the “Fair Tax,” is politically infeasible because it would punish senior citizens who have paid income taxes all their lives and will face a consumption tax as they spend their retirement savings. Still, Norquist said, the attention on 9-9-9 has been a positive.

“Cain has done a very good thing in dramatizing the flaws of the present tax code -- it’s too redistributionist and taxes are too high,” Norquist said.

Chris Chocola, a former congressman and president of the archconservative advocacy group Club for Growth, praised Cain's political skills but expressed similar concerns with a value added tax.

“We don’t think it’s perfect,” he said of 9-9-9. “We haven’t endorsed it, but we think it’s worth examining and learning more about it.”

Though he is campaigning as the ultimate outsider, having never held political office, Cain is known inside the Beltway. He led the National Restaurant Association lobby in the 1990s, and his 2004 U.S. Senate run and radio platform made him one of the country’s most prominent black Republicans, Fratto said.

But in the truest sign of allegiance -- writing a check -- Cain has yet to make inroads. A Washington Post analysis of campaign finance reports last week showed that no lobbyists donated to Cain through Sept. 30, whereas more than 100 lobbyists donated to front-runner Mitt Romney. Just one political action committee, for the Charlotte-based hospital system MedCath, has donated to Cain. The Cain campaign has boasted of booming fundraising this month, but he still trails most of his rivals in the money race.

Funding has been less important so far, as candidates’ popularity has been primarily driven by debates and news media appearances. But Fred Barnes, conservative commentator and executive editor of the Weekly Standard magazine, said when the real voting starts in January, money will take on a heightened importance. Campaigns will air costly television advertisements and employ sophisticated organizations in early primary states.

“It’s about the quality of the candidate, not necessarily the quality of the debate performer,” Barnes said. “Herman Cain still has a lot to prove.”

Republican consultant David Winston, an adviser to Gingrich when he was speaker of the House, said Cain's Washington blitz is part of an effort to show the skeptics that he belongs in the top tier.

"He’s got to respond to the questions raised around 9-9-9," Winston said. "Once that hurdle’s done, the next step is: OK, people like the idea or think there’s some plausibility to it, then he’s got to define how’s he going to get it done."

But Rep. Jack Kingston, a Savannah Republican, said Cain should not put too much concern into how his stock is faring in Washington.

"No," Kingston said, when asked if the Beltway is taking Cain seriously. "But the Beltway doesn’t know him, and I think sometimes the Beltway’s the last to know anyhow."