Republican U.S. presidential candidate Donald Trump addresses a crowd during a presidential forum in Aiken, South Carolina, Dec. 12, 2015. Reuters

Is Donald Trump a big liar? That's what fact-checkers across the nation are alleging. The Washington Post's Fact Checker listed three false claims made by Trump on the campaign trail this year on a list published Monday called "The biggest Pinocchios of 2015." PolitiFact, a fact-checking news site, asked readers to pick "the most significant falsehood of 2015" from a list of 11 statements made by political leaders. Trump had uttered four of the statements, more than any other figure, including "The Mexican government ... they send the bad ones over" and "I watched in Jersey City, N.J., where thousands and thousands of people were cheering." The latter claim of Muslims celebrating the Sept. 11, 2001, attacks earned him a "Pants on Fire" rating from the site.

"Most politicians drop a claim after it has been fact-checked as false. But Trump is unusual in that he always insists he is right, no matter how little evidence he has for his claim," the Washington Post noted in its list of false claims. "Frankly, it’s really not interesting to fact check The Donald, as his assertions are so easily debunked."

The Post also slammed Democratic presidential front-runner Hillary Clinton for defending her husband’s signing of the anti-gay Defense of Marriage Act as a move to prevent a constitutional ban on same-sex marriage. Clinton's presidential campaign has adopted a pro-LGBT rights stance by trying to distance itself from Bill Clinton's administration.

"Hands up, don't shoot" was ruled another big falsehood. The phrase became a rallying cry for protests after the fatal shooting of Michael Brown, 18, by white police officer Darren Wilson in Ferguson, Missouri, in August 2014. Various investigations found Wilson acted out of self-defense and was justified in killing Brown, who did not actually say "don't shoot" before he was killed, the Washington Post reported.

PolitiFact also slammed Clinton for making false statements on the campaign trail, rating her comments that the gun industry is "the only business in America that is wholly protected from any kind of liability" as false. The site also called out Republican candidate Ben Carson for his statement that "German citizens were disarmed by their government in the late 1930s," which allowed the Nazis to "carry out their evil intentions with relatively little resistance."