Tom Tancredo’s retirement will be felt in the House among the core group of illegal-­immigration critics.

But a spokesman for the House Immigration Reform Caucus said Tancredo, the founder of the group, divested himself of leadership responsibilities on the issue in Congress a long time ago to make his run for president.

Tancredo, R-Colo., has kept up the fight outside Washington, however, making it the focus of his presidential bid.

“Obviously, we are losing one of our leading voices on the immigration issue,” said Kurt Bardella, a spokesman for California Republican Brian P. Bilbray, who took over for Tancredo as chairman in February. “We are losing a passionate voice on the issue, but hopefully he will be moving on to bigger and better things.”

Under Tancredo’s leadership, the caucus grew to more than 100 members and was instrumental during the 109th Congress in opposing the Senate and President Bush on a comprehensive immigration plan that would have allowed millions of illegal immigrants to become citizens.

The transition to Bilbray’s leadership has been smooth. The caucus now numbers 110 members, has hired an executive director and is pushing as hard as ever for tougher border security and immigration laws by targeting amendments in many pieces of legislation moving through Congress.

“Certainly, the success we have had, the foundation was built by Tancredo,” said Bardella. “His presence will be missed.”