“This has been a unified approach, rather than a divisive approach,” says Douglas Holtz-Eakin, the president of the American Action Forum. “And it reflects six or seven years of accumulated wisdom, that it will fall to conservatives to fix this problem.” …

That wisdom also reflects a keener grasp of how Barack Obama operates. The president wants citizenship for illegal immigrants, but he cares little for Republican concerns about the border, or fairness, or guest workers. His executive order stunt granting temporary status to young immigrants shows that he would happily “reshape the system by executive fiat, which is the last thing any conservative should want,” notes Steven Law, president and CEO of American Crossroads.

The 2007 effort was driven by George W. Bush and John McCain—both of whom at that time inspired deep grass-roots ire. This time around, Mr. Rubio has the conservative street cred to draw in allies, while his outreach and his vow to steadily improve the Senate bill has given the process the room to proceed.

Nevertheless, immigration reform will be hard, maybe even impossible. It might still devolve into a conservative argy-bargy. Because there is a split in the GOP, one that is highlighting an important philosophical divide that transcends stale categories like “conservative” or “moderate” or “anti-amnesty” or “pro-business.”