Attorney General Mike DeWine, a former US senator who was backing Mitt Romney for president, has changed his endorsement and embraced Rick Santorum for the nomination.

ABC News:

The prominent Buckeye State Republican threw his support behind presidential candidate Rick Santorum on Friday afternoon, switching his allegiance from Mitt Romney to the former Pennsylvania senator.

"To be elected President, you have to do more than tear down your opponents," DeWine said in a statement.  "You have to give the American people a reason to vote for you -- a reason to hope -- a reason to believe that under your leadership, America will be better.  Rick Santorum has done that.  Sadly, Governor Romney has not."

DeWine made the official the announcement on Friday in front of the Ohio State House in Columbus. There he candidly admitted he "was wrong" to have endorsed Mitt Romney four months ago and he was even more candid about why.

According to DeWine, Romney has shown an "astounding inability to provide voters with a rationale to support him."

As for Santorum, "People like him -- he's human!" DeWine said.

He cited Romney's "massive financial and organizational advantage" as one of the reasons he previously supported the former Massachusetts governor's presidential bid.

Evidently pleased by DeWine's scathing critique of Romney, Santorum said he only wished his wife could have been in Ohio to attend the endorsement event: "I wish Karen could have heard that," he said.

Santorum will become the third presidential candidate DeWine backed during the primary season. The former U.S. Senator who served alongside Santorum in Washington, originally endorsed Tim Pawlenty before moving to Romney after Pawlenty dropped out of the race.

DeWine is one of the most popular politcians in the state and Romney, already trailing Santorum in Ohio's March 6 primary, could ill afford to lose him. It is contributing to the building narrative that Romney is sinking, largely as a result of what DeWine pointed out; he has been unable to convince people he has a rationale for running for president.

If Santorum wins both Michigan on February 28 and Ohio on March 6, Mitt Romney will be dead in the water with little to recommend that he continue the race.