Colorado Rep. Tom Tancredo said Monday that he would not seek a sixth term in the House in next year's elections, but he would remain a presidential candidate seeking the Republican nomination.

"I think my task, my chore, whatever it is, my service, in the House of Representatives, is completed," Tancredo said, speaking by phone with FOX News Monday morning.

Tancredo — the perennial illegal immigration foe — said his decision has "been a long time coming."

Tancredo said that when he first ran for Congress, he pledged to stay only for three terms, but during his second term, he told his constituents that he would have to break the promise to fight illegal immigration.

"I would go on the floor of the House night after night speak, and no one else would ever come up, and I'd offer amendments one after another for years and no one would ever — I mean the most we'd get is 80 or 90 votes, and things have changed dramatically," Tancredo said.

"We're now a lot of people in the House of Representatives ... that I can hand that baton to, and do so with knowledge that they will fight for this issue," Tancredo said, adding, "I have helped make it that way, I think, at least I hope, and I'm going to continue to do that of course during our discussions of, with this campaign for president."

Asked if he was frustrated with politics in the House, he said he was pleased with the amount of attention illegal immigration has achieved — noting that one amendment of his that was virtually ignored years ago, was agreed to easily this year by voice vote.

"No, it isn't a frustration with it. ... I love public policy, and I hope to be doing it a long time as president, but if that doesn't work out it doesn't matter, there are other things."

National Republican Congressional Committee Chairman Tom Cole said Tancredo would be missed.

"Tom Tancredo is a dedicated public servant who is both fervent in his beliefs and devoted to his country and to his home state of Colorado . Upon his retirement from the U.S. House, the people of Colorado ’s 6th Congressional District will lose a strong and passionate representative," Cole said.

Tancredo is known primarily for his staunch opposition to illegal immigration, which is the central pillar of his campaign platform, but the issue hasn't helped his campaign pull away from the basement-dwelling poll numbers.

In the most recent FOX News/OpinionDynamics poll, 2 percent of registered Republican voters said they would pick Tancredo, followed only by GOP iconoclast Ron Paul in the field of eight candidates. The Oct. 23-24 poll included 900 registered voters, 303 who identified themselves as Republicans.