If the 2008 presidential election turns out to be close, a few thousand votes here or there could sway the results—so both parties are working to stop a third-party bid.

Democratic strategists are concerned that a challenge from the left might undermine a centrist Hillary Rodham Clinton candidacy. Republican strategists are equally worried that if Rudy Giuliani, Mitt Romney, or John McCain becomes the nominee, he might face a challenge from a right-wing anti-immigration candidate.

Who might play the role of spoiler in 2008?

Republicans around McCain have been watching CNN’s Lou Dobbs, who has been gaining popularity on TV with his anti-immigrant, anticorporate comments and segments like “Broken Borders” and “Exporting America.” It isn’t lost on political watchers that Dobbs is urging his viewers to switch their affiliation to “independent” to protest the corporate backing of both parties.

Author/globalization expert Ted Fishman says Dobbs is offering “the most direct assault on American big business by an establishment figure since Dwight D. Eisenhower took on the military-industrial complex.”

New York City mayor Michael Bloomberg is another strong contender for a center-right independent bid—he could write any size check to fund a campaign, and a bipartisan team at Unity ’08 is working to line up ballot access that might ease the way for a third-party run. Bloomberg has been reaching out across the aisle to Democrats like Al From, who heads the centrist Democratic Leadership Council.

On the left, rebel union leader Andy Stern, head of the powerful Service Employees International Union that led the breakup of the AFL-CIO, could leave the Democrats if he feels workers aren’t being represented. Stern’s made no secret of his disdain for both parties, and his 1.8 million members would provide the army for a grassroots outside-the-system bid. In a not-so-subtle warning, Stern is scheduling a trip to New Hampshire and Iowa at the end of January as part of a book tour.