What an election: The one-time mayor of Ellis Island, grandson of Italian immigrants, has to make nice with the modern-day Know Nothings if he wants a shot at his party’s nomination for the presidency. Mayor Giuliani gets immigrants. He’s lived their dreams. He’s governed their city. He’s won their hearts and their minds and their votes. But now he must walk a razor’s edge between advocating sensible immigration reforms on one side and demonizing immigrants as criminals and invaders on the other.

Having transgressed from conservative orthodoxy irreparably on one issue, abortion, Mr. Giuliani has been pursuing a strategy of walking back his transgressions on other issues — all the while being careful to avoid the whiplash effect that has hobbled Mitt “Flip” Romney. On gun control, he hasn’t apologized for his actions in New York City, but he’s said regulation of guns should be left to states and localities. On civil unions, he’s claimed that his past support was based on imprecise language and that he really only supports domestic partnerships.

Now we come to immigration. His problem here is just how far he stuck his neck out for illegal immigrants while mayor of New York City. Take this, from a 1994 press conference: “Some of the hardest-working and most productive people in this city are undocumented aliens,” Mr. Giuliani said. “If you come here and you work hard and you happen to be in an undocumented status, you’re one of the people who we want in this city.”

Powerful stuff. Reminiscent of President Bush’s old slogan that family values don’t stop at the Rio Grande. But not a sentiment that will play well in the redder parts of the red states.

Or how about this, from a 1996 speech to Harvard’s Kennedy School of Government: “We’re never, ever going to be able to totally control immigration to a country that is as large as ours, that has borders that are as diverse as the borders of the United States, and as a society that wants to be a country that values freedom.”

Now the second of the Twelve Commitments on which Mr. Giuliani is campaigning is that he “will end illegal immigration, secure our borders, and identify every non-citizen in our nation.” To these ends, he now supports a border fence in conjunction with a “high-tech border” and a national biometric ID card.

An Olympic-level flip-flop? In fairness to the former mayor, there’s a decent case to be made that his 1990s positions and his 2000s positions are compatible. First, there’s the difference between federal and local responsibility. At the same 1996 conference at which Mr. Giuliani defended New York City’s Executive Order 124 — which stops city agencies from reporting illegal immigrants to the federal immigration authorities — he also declared that “preventing illegal immigration is the job of the federal government. The United States has to do a lot better job of patrolling our borders.” He had a city with a high crime rate to bring down, he can argue, and he needed illegal immigrants to trust the police and cooperate in investigations. As president, he’d make the border the priority.

The biggest shift in Mr. Giuliani’s thinking seems to have come on the issue of whether it’s even possible to control the border. Here, he credits advancing technology for his change of mind, in conjunction with the increased threat we face as a nation after September 11, 2001.

The problem for the mayor, however, is that if his views really haven’t changed all that much since the mid-1990s, all the anti-immigrant folks he’s trying to court have little reason to trust him. He does, after all, still support the sort of “path to citizenship” that got Senator McCain tarred and feathered and all but thrown out of the Republican primary. And he also supports a big increase in legal immigration.

The danger is that Mr. Giuliani will end up in a rhetorical race to the bottom with Mr. Romney for who will be toughest on immigrants. And it’s hard to win a pander-off with Mitt Romney.

Mr. Giuliani’s first radio ads on the subject already strike a worrying tone, focusing on illegal immigrants who have committed violent crimes. While the policy he’s pushing — deporting such criminals ahead of, say, busboys — is sensible, a segment of the right has been trying to paint all illegal immigrants as dangerous, violent criminals for years.

These are the tactics of the modern-day Know Nothings, and a New York City mayor ought not be lending them a hand. He ought to be showing them the door.