The ink was still wet on a bipartisan immigration deal backed by Sen. John McCain, R-Ariz., when former House Speaker Newt Gingrich tried to make opposing the landmark legislation a litmus test for anyone eyeing the White House in 2008.
"I am so much in opposition to this bill that I want to make it very clear," said Gingrich Thursday on Sean Hannity's radio program. "If I were president, I would veto this bill. I think it's that bad. And I would challenge everybody currently running for president to indicate whether they would sign or veto this bill -- nothing in between."
"This is a terrible sellout of American security," Gingrich concluded.
Just this week, Gingrich told ABC News' Diane Sawyer on "Good Morning America" that there is a "great possibility" that he will enter the presidential race later this year.
Two of McCain's top-tier rivals -- former Massachusetts Gov. Mitt Romney and former Tennessee Sen. Fred Thompson -- have already come out forcefully against the immigration measure which would fortify the border, toughen work site enforcement and change the way future immigrants are selected while offering a multistep path to citizenship for millions of illegal immigrants currently in the United States.
Romney, who seemed open to earned legalization just a year and a half ago, denounced Thursday's plan as "amnesty" in a statement released just hours after the bipartisan Senate deal was announced.
"Any legislation that allows illegal immigrants to stay in the country indefinitely, as the new 'Z-Visa' does, is a form of amnesty," said Romney. "That is unfair to the millions of people who have applied to legally immigrate to the U.S."
For the past nine months, Romney has pointed to McCain's support for earned legalization as a defining contrast between them.
Earlier this week, he confronted McCain on the issue in person for the first time.
"My fear is that McCain-Kennedy would do to immigration what McCain-Feingold has done to campaign finance and money in politics, and that's bad," said Romney at Tuesday's debate in Columbia, S.C.
When questioned at that same debate about his previous pro-earned legalization comments, Romney said that he would not bar illegal immigrants from applying for permanent residency after they were asked to go home.
He added, however, that they should not get "any advantage" by having come to the United States illegally. "That's the key part of what I objected to in McCain-Kennedy," said Romney.
The other top-tier McCain rival who opposes Thursday's immigration deal is Thompson.
"With this bill," said Thompson, in a statement also released within hours of the Senate's announcements, "the American people are going to think they are being sold the same bill of goods as before on border security. We should scrap this bill and the whole debate until we can convince the American people that we have secured the borders or at least have made great headway."
Thompson, who backed McCain for president in 2000, is not officially in the presidential race. But he has been making speeches around the country and is expected to throw his hat into the ring as early as June or as late as September.
One top Republican who punted Thursday was Rudy Giuliani, the former New York mayor who sits atop the field in public opinion polls.