With three weeks to go until Election Day, and after a week of harsh personal attacks on his Democratic opponent, Republican presidential candidate Sen. John McCain continues his slide in national polls. And he's starting to get unsolicited advice from leading members of his own party.

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The latest national poll, from Washington Post-ABC News, shows Sen. Barack Obama leading McCain 53 percent to 43 percent among likely voters. And 64 percent of respondents view Obama in a positive light, an improvement of 6 percentage points compared to September. More than a quarter said they think worse of McCain as a result of the debates, the third and last of which comes Wedenesday.

Some marquee names in GOP circles are questioning McCain's ability to mount a comeback, questioning his tactics and even his campaign's main thrust in a White House race increasingly focused on economic turmoil.

"He has to make the case that he's different than Bush and better than Obama on the economy," said former House Speaker Newt Gingrich, one of more than a dozen prominent Republicans who in interviews during the past week expressed concern over the course of McCain's bid. "If he doesn't win that case, it's all over, and it's going to be a very bad year for Republicans."

Several Republicans said McCain needs to strike a balance in his tone -- appearing presidential while also questioning Obama's readiness to serve and judgment to lead. And, several said McCain should close the campaign on an honorable note.

These Republicans, speaking on condition of anonymity to avoid angering McCain, said the campaign's attempt at this late stage to plant doubts about Obama's associations with 1960s-era radical William Ayers, makes the 72-year-old McCain come off as angry, grouchy and desperate.

McCain's campaign sent mixed signals on Monday about whether the candidate will offer new proposals to address the financial crisis.

On Sunday, Sen. Lindsey Graham, R-S.C., a top adviser to McCain, said the presidential candidate was considering a reduction in taxes on investments, including a possible cut in the capital gains tax. But campaign spokesman Tucker Bounds said McCain would not announce any specific proposals during campaign stops Monday in Virginia, North Carolina and Pennsylvania. He added, "We will likely have further proposals this week as economic news and conditions change."

McCain refused to answer a reporter's question Sunday about what plans he might be considering.

Addressing several dozen volunteers at his campaign headquarters outside Washington, McCain promised some of his signature "straight talk" about the state of the race. National and many battleground state polls have shown him trailing Obama amid the deepening market crisis.

"We're a couple points down, OK, nationally, but we're right in this game," McCain said to cheers. "The economy has hurt us a little bit in the last week or two, but in the last few days we've seen it come back up because they want experience, they want knowledge and they want vision. We'll give that to America."

McCain said he and running mate Sarah Palin would continue campaigning hard in the three weeks left before Election Day, in places like Ohio, Pennsylvania, New Mexico, Nevada and Colorado. The two planned a joint appearance Monday in Virginia, a Republican stronghold turned battleground this time.

"We're going to spend a lot of time and after I whip his you-know-what in this debate, we're going to be going out 24/7," McCain said of Obama.

The two men will debate Wednesday at Hofstra University on Long Island, N.Y. CBS News anchor Bob Schieffer will moderate the 90-minute forum.

Still, McCain promised to run a "respectful" campaign in the weeks to come.

"I respect Sen. Obama, we will conduct a respectful race and be sure everyone else does, too. But there are stark differences between us," McCain said.

Graham, on CBS' "Face the Nation," said the GOP candidate was considering policy proposals that would cut taxes on investments.

"I think it goes along the lines of now's the time to lower tax rates for investors, capital gains tax, dividend tax rates, to make sure that we can get the economy jump-started," Graham said on CBS' "Face the Nation." "It will be a very comprehensive approach to jump-start the economy by allowing capital to be formed easier in America by lowering taxes."

McCain already has laid out proposals to address the crisis, including a $300 billion plan for the federal government to buy distressed mortgages and renegotiate them at a reduced price.