Mitt Romney racked up another major endorsement on Sunday, with freshman Wisconsin Sen. Ron Johnson backing him on NBC’s “Meet the Press” just days before that state’s Republican presidential primary.

The senator said Romney “fully understands the gravity of our financial situation” because of years working in the private sector.

“I  never did intend to endorse anybody, but I've had the opportunity to meet with Gov. Romney over the last couple weeks, had long phone conversations with him,” Johnson said. “I've come away from those conversations fully convinced that Gov. Romney is the person to lead our party, to lead our nation.”

It’s the latest blow to Rick Santorum’s camp, as Romney also racked up support last week from House Budget Committee Chairman Paul Ryan (R-Wis.) and Sen. Marco Rubio (R-Fla.), in addition to the blessing of former President George H.W. Bush.

“Everybody's entitled to a mistake in their life,” Santorum said on “Meet the Press.” “Rubio and Ryan are pretty young. They'll recover from it.”

Sen. Chuck Schumer (D-NY), also appearing on the show, interpreted the Rubio endorsement as a sign of weakness.

“They're trying to make amends for the horrible shape they're in with Hispanic voters,” he said. “Hispanic voters are hostile to Mitt Romney and the Republicans because of their anti-immigration stands.”