Sen. John Kerry (D-Mass.) wants Colorado Sen. Michael Bennet (D) to "hit … back harder" against his Republican challenger.

Jane Norton, a Republican Colorado Senate candidate, recently put up a Web video that criticizes President Barack Obama's handling of the war on terrorism. 

"The liberals in Washington seem to have forgotten ... (sound of jet engines over a black screen symbolizing 9/11) ... But we haven't. Let's win the war on terror," Norton says in the video.

"This is about the same dirty campaign tactics I've seen a hundred times, and they don't just make my blood boil, they demand action," Kerry wrote in a fundraising pitch to Bennet's supporters Friday. "Like other desperate politicians who've deployed the tactics of fear and smear, she has sunk to invoking images of our heroic service members to launch a thinly veiled attack on" Bennet and Obama.

Kerry recalled the time he came under so-called "Swiftboating" attacks. "I learned a lot from that experience," he wrote. "The lesson: they hit you, hit them back harder — make them pay a price."

Norton has been watching her lead in the polls slip against Weld County District Attorney Ken Buck (R). Observers believe she is trying to shore up her base of support ahead of the August Republican primary.