Barack Obama's getting a lot of flak this week from progressives on issues ranging from warrentless wiretapping to Iraq to abortion. But he's not the only presidential candidate with "base" issues.

Conservatives are beginning to mutter that John McCain is backsliding from the white flag he raised on comprehensive immigration reform in order to obtain the Republican nomination.

National Review's Byron York, writing in the Hill today, raised his own red flag in a column titled: "The Ultimately Incorrigible John McCain."

Noting McCain's primary-period contrition for his championship of comprehensive reform, York complains:

Now we’re seeing the old McCain. He’s been talking about comprehensive immigration reform again lately, and he hasn’t been terribly careful about assuring audiences that the borders will be secured first, and only then will other aspects of reform go forward.

Take his appearance last week before the National Association of Latino Elected and Appointed Officials. In prepared remarks, he spoke of securing the borders. But later, when asked whether comprehensive reform -- not just border-securing enforcement -- would be one of his top priorities in his first 100 days in office, McCain said: "It will be my top priority yesterday, today and tomorrow."

That didn’t really sound like securing the borders first.

York goes on to say that McCain did better during this week's throwdown with Obama in an appearance before the League of United Latin American Citizens. But that's the same appearance where McCain got panned for failing to talk much about immigration, instead offering a Spanish-accented version of his stock economic speech. Still, conservatives, who once thought immigrant-bashing would be the great wedge issue of 2008, will be watching McCain closely for future heresies, as York makes clear:

This is serious stuff. McCain made a promise to the voters who chose him over his rivals in the Republican primaries. If it appears that he is going back on that promise, or wobbling, or slipping into the old McCain who nearly lost the nomination, he’ll be in trouble.