As has often been the case with Delaware Sen. Joseph Biden’s political career, his semi-official entrance into the 2008 presidential field over the weekend was greeted with a mix of optimism and skepticism among Democratic consultants and party strategists.

Biden chose CBS’ “Face the Nation” to acknowledge that his “intention now is to seek the nomination,” before quickly adding that he would not make a final decision until the end of the year.

The consensus gleaned from a series of interviews with Democratic campaign operatives was that while Biden makes a compelling first impression and has the charisma many would-be candidates lack, his staying power remains a real question.

“As a profile, especially compared to [Massachusetts Sen. John] Kerry, [New York Sen. Hillary Rodham] Clinton and [former North Carolina Sen. John] Edwards, he’s all you could hope for,” said one high-level Democratic strategist. “But, mechanically, he’s got a huge lift.”

The biggest challenge before Biden, according to knowledgeable party sources, is to prove that he can raise the tens of millions necessary to stay within shouting distance of the top-tier candidates.

Biden has always been a solid fundraiser, spending $3.2 million and $2.5 million on his 2002 and 1996 re-election races, respectively.

At the end of April, Biden showed $675,000 in his Senate account after raising $213,000 in the first three months of the year.

During his aborted run for the presidency in 1987, Biden was one of the strongest fundraisers in the field — raising nearly $4 million before dropping out in late September amid plagiarism allegations.

Times have changed in the intervening years.

By conservative estimates, a serious Democratic candidate for president will need to raise $40 million to have a shot at the nomination.

That hefty pricetag is born of a compressed primary calendar, which will force candidates to spend heavily in a number of states simultaneously, as well as the likelihood that all the major candidates will reject matching funds from the Federal Election Commission — a move that will allow them to raise and spend unlimited sums in early primary and caucus states.

“It would be shocking if someone who stayed within the [financing] system was nominated,” said one Democratic consultant not affiliated with any of the candidates mulling a bid.

Whether Biden can make the leap from $4 million to $40 million is an open question; his lack of a national fundraising base coupled with his roots in Delaware, not a state that can produce millions in donations for a native son, may not bode well.

If money could be Biden’s Achilles heel, his foreign policy credentials are far and away his biggest potential strength.

From his perch on the Senate Foreign Relations Committee, Biden has long been one of the leading Democratic voices on international affairs, a position that has been enhanced since the start of the war in Iraq.

Biden supported the resolution authorizing the use of force in Iraq and also backed President Bush’s $87 billion request to fund the operations in Iraq and Afghanistan.

He has, however, been a frequent critic of the Bush administration’s handling of the aftermath of the invasion and emphasized the need to set up benchmarks for success in Iraq.

Biden will speak at the Brookings Institution today in a talk titled “U.S. Policy in Iraq: Rhetoric vs. Reality.”

“Depending on how Iraq plays out and where it is in the public consciousness, it will be important to have somebody who can speak with real authority on it,” said Steve Elmendorf, a Washington lobbyist with Bryan Cave Strategies.

Added Democratic strategist Chris Lehane:  “Biden along with [Hillary Rodham] Clinton, Gen. Wesley Clark and [New Mexico Gov.] Bill Richardson are able to pass the ‘tough on national security’ credential that should be a pre-qualification for all Democratic presidential candidates.”

The X-factor for Biden — as it has been for the entirety of his political career — is his personality.

“He surely has a big leg up on the charisma and personality factor,” a Democratic consultant said.

Put another way, Biden passes the “Imus test,” in the words of Lehane. A regular guest on radio talk show host Don Imus’ morning program, Biden has acquitted himself well in the back-and-forth repartee of the show, showing in the process that he is not just another wooden politician.

The Delaware Senator is clearly positioning himself as the renegade in the Democratic field, a politician willing to speak his mind regardless of the consequences.

Sound familiar?

“He fashions himself as the Democratic [Arizona Sen. John] McCain,” said one Democratic consultant. “He is trying to use his candor and straying off course as an advantage.”

McCain built a movement during the 2000 presidential primaries thanks to his willingness to provide “straight talk” to voters on controversial issues. Despite his defeat at the hands of Bush, McCain is currently the most popular politician in America and considering a 2008 run.

In recent weeks, Biden has publicly disagreed with comments made by Democratic National Committee Chairman Howard Dean and admitted in an interview following his “Face the Nation” appearance that he may be too “muscular” on foreign policy to win a Democratic presidential primary.

Biden’s proclivity for off-the-cuff remarks presents a double-edged sword for his candidacy. “The way he got in [to the race] speaks to some of his appeal and some of the downside,” said one high-level campaign strategist.