From core issues to the ephemeral, both presidential candidates have managed to engineer their share of flip-flops. While many have cropped up in attack ads, several are more glaring than others. Here's a guide to some of this year's most high-profile reversals, rated on a scale from 1 (a little waffling) to 5 (a complete 180).

John McCain

President Bush's tax cuts

The flip: In 2001 and 2003, McCain voted against President Bush's tax cuts, saying they were too large, would generate deficits, and favored the wealthy. The flop: In 2006, he voted to extend them and, as a candidate, firmly supported the cuts (which are set to expire at the end of 2010). The bottom line: McCain has explained it by saying that repealing the cuts now would feel like a tax increase and could further harm an economy in crisis, but it's still nearly a full reversal. The rating: 4

Banking regulations

The flip: McCain, a longtime deregulator, supported a 1999 bill authored by Sen. Phil Gramm that stripped away years of stringent banking regulations. Gramm is a longtime McCain friend and economic adviser. The flop: Amid a $700 billion bailout of financial institutions, McCain is calling for more oversight. The bottom line: With 90 votes in the Senate, the banking bill was bipartisan. Times have changed, but McCain's advocacy of deregulation—including a 1990s push for a moratorium on all new regulation—has been consistent. The rating: 5

Offshore drilling

The flip: During his 2000 presidential run, McCain supported a moratorium on offshore oil drilling. The flop: When gas hit $4 a gallon, he called for lifting the restrictions "to put our own reserves to use." The bottom line: McCain says the psychological boost of new exploration could help lower prices, but as recently as May, he called it a temporary fix that wouldn't be available soon. The rating: 3

Torture

The flip: A victim of harsh treatment as a POW in Vietnam, McCain has long condemned torture. The flop: McCain voted against a 2008 measure that would have forced the CIA to abide by the Army Field Manual, which prohibits inhumane measures. The bottom line: McCain said he voted against the bill because legislation he helped pass already bars the CIA from using cruel techniques, but questions remain about the Bush administration's interpretation of the law. The rating: 1

Barack Obama

Public financing of campaign

The flip: Obama said last year he would take part in the traditional public financing program for the general election. The flop: In June, Obama opted out of the federal system. The bottom line: Obama chose to take advantage of his phenomenal fundraising. He has hauled in over $450 million, making a flip-flop inevitable. The rating: 5

Offshore drilling

The flip: Obama is a longtime opponent of additional offshore drilling. As recently as July, his campaign said lifting the ban would "merely prolong" failed energy policies. The flop: In August, after the spike in gas prices, Obama changed his tune and said he'd be open to limited new drilling. The bottom line: The switch was conditioned on being able to use drilling as leverage to win renewable energy provisions. The rating: 2

Domestic electronic surveillance

The flip: One year ago, a spokesman for Obama said he would filibuster legislation to bolster the government's authority to conduct domestic surveillance if the bill granted immunity to telecom companies that participated in the Bush administration's wiretapping efforts. The flop: In July, Obama voted for the Foreign Intelligence Surveillance Act reform bill, which grants that immunity. The bottom line: He did try to alter the bill, but when that failed, he voted for the measure. The rating: 4

Iraq withdrawal timetable

The flip: In January 2007, Obama introduced a bill that would have removed all U.S. combat troops from Iraq by the end of March 2008. During the campaign, he has pledged to remove combat forces within 16 months of taking office. The flop: Over time, he has said he might "refine" that pledge based on advice from commanders and the situation on the ground. The bottom line: His original proposal allowed for some flexibility on the timetable, and his aides say that Obama would keep up to 60,000 support troops in Iraq past the deadline. Either way, new qualifiers keep emerging. The rating: 3

Just the Facts

This year's campaign has certainly seen its share of exaggerations, distortions, and even outright lies. A number of watchdog groups are trying to police the candidates. Here are a few of the best: OpenSecrets.org, run by the Center for Responsive Politics, tracks campaign finance and lobbying. The Annenberg Public Policy Center's Factcheck.org researches the veracity of the campaigns' claims. Votesmart.org is a grass-roots site with in-depth research on the candidates and their policies.