Sen. John McCain has endorsed SB 1070, the illegal-immigration omnibus legislation that the Arizona Senate is scheduled to vote on this afternoon.

Politico reports:

Sen. John McCain has endorsed a tough Arizona anti-immigration bill that will let police arrest people who aren’t carrying identification, the latest move in McCain’s rightward shift in advance of a tough Republican Senate primary this summer.

“I think it’s a very important step forward,” McCain said Monday. “I can fully understand why the legislature would want to act.”

It’s a dramatic switch for a senator who supported comprehensive immigration reform with Democratic lion Sen. Ted Kennedy (D-Mass.) just four years ago. McCain is facing a primary challenge from the right in former Rep. J.D. Hayworth.

Under the Arizona law, which passed the state House last week and is expected to be signed by Gov. Jan Brewer (R), police can arrest anyone

on “reasonable suspicion” that they are an illegal immigrant. If they’re not carrying a valid driver’s license or identity papers, police can arrest them.

Under current law, illegal immigration is a federal crime, and state law enforcement officials can only ask about it if a person is suspected of another crime.