As the presidential race heads into the final four weeks, commentators are saying that the campaigns are taking the gloves off.

The latest ad for Sen. John McCain features Sen. Barack Obama's links to a member of the 1960s radical group, The Weathermen, and his association with the violent group's founder, Bill Ayers.

The latest ad for Obama responds by reminding voters of McCain's involvement with the Keating Five scandal and the savings and loan crisis of the late 1980s.

These ads are only the latest reasons for voters to dig deeper for the truth or do some research for the whole story. Luckily, interested voters don't have to do all the work themselves. Two popular Web sites providing such services are FactCheck.org and Politifact.com.

FactCheck is a non-partisan organization affiliated with the Annenberg Public Policy Center of the University of Pennsylvania.

Its latest home page features an outline of inquiries, offering deeper explanations behind the simple summary. The most recent entries include:

n Fact-checking the Biden-Palin debate — The candidates were not 100 percent accurate, to say the least.

n More Social Security spin —An Obama-Biden ad misrepresents the Social Security plan McCain supported. Again.

n Cause of the economic crisis — Moveon.org blames McCain advisers. He blames Obama and Democrats in Congress. Both are wrong.

n Obama's stem cell spinning —His radio ad is wrong: McCain still supports federal funding for stem cell research.

n Obama's trade trickery — An Obama ad implies that a Pennsylvania plant sent jobs overseas and says that McCain is to blame. That's wrong.

n Not coming clean on coal —A McCain-Palin ad claims the Obama-Biden ticket opposes clean coal. Not true.

And more misleading claims by both campaigns and all four candidates can be found under the heading "The Whoppers of 2008."

On the Web site of Politifact.com, a group affiliated with the St. Petersburg Times newspaper and Congressional Quarterly magazine, there is a section called "The Attack File," where the attack candidate or campaign is named along with the target candidate. And next to each campaign attack ad is a rating, from mostly true to half-true, to barely true and all the way to "pants on fire" (as in the childhood taunt "Liar, liar, pants on fire").

While these Web sites can be entertaining, they also are, and have been, important resources for voters watching the presidential campaign and wanting to separate fact from fiction or spin. These Web sites also were helpful during the primary races to determine which charges or claims by Obama and Sen. Hillary Clinton were true and which were false. It's not an easy job for the average voter.

As the late Sen. Daniel Patrick Moynihan has been credited with saying, "Everyone is entitled to his opinion, but not his own facts." This should not have to be applied to candidates for president, but clearly it does.

The final month of a presidential campaign is a time when new negative or attack ads and stinging stump speech statements are coming out just about every day.

The fact-checking Web sites and some national in-depth reporting have revealed that both campaigns are guilty of bending facts, spinning the truth or, in some cases, just plain lying.

It's a sad state of affairs that such fact-checking is necessary — many would argue that major news organizations should be doing a better job of separating fact from fiction. But it's helpful to know that voters wanting to understand the truth have resources close at hand that will reveal the full story and stop the spin.