Washington ? A year ago, when Sen. Sam Brownback, the conservative Kansas Republican, co-sponsored legislation that would have allowed millions of illegal immigrants to seek U.S. citizenship, he was attacked as a liberal.

This year he’s running for president, and now liberals are attacking him for flip-flopping on immigration.

“I understand when people are seeking re-election or going to a higher office, they do seem to have a change of heart,” said Mary Lou Jaramillo, the president and chief executive officer of El Centro Inc., a Kansas City, Kan.-based group that aids immigrants.

Brownback, she said, isn’t alone. Although both political parties acknowledge the nation’s immigration policy is broken, the 2008 presidential campaign is complicating efforts to fix it.

The Senate is debating a bill that would legalize millions of undocumented immigrants and create a guest-worker program for as many as 200,000 low-skilled workers a year. But while the Bush administration supports it, many Republican candidates are distancing themselves from any legislation that the GOP’s conservative base might consider soft on illegal immigrants.

Brownback and another of this year’s Republican presidential candidates, Arizona Sen. John McCain, teamed last year with Democratic Sen. Edward Kennedy of Massachusetts to sponsor legislation to provide better border security and create a guest-worker program for 12 million illegal immigrants.

Kennedy, who made his lone presidential bid 27 years ago, is among the sponsors of this year’s bill.

Brownback and McCain aren’t.

Brownback declined repeated requests to be interviewed for this story.

In a speech Wednesday on the Senate floor, he lamented the growing number of illegal immigrants in the nation, saying it’s tripled to 12 million from 4 million in 1987.

“Some people think that the solution is to grant undocumented immigrants amnesty : but that won’t work,” Brownback said.