WASHINGTON -- Sen. Ron Johnson (R-Wis.) endorsed Mitt Romney on NBC's "Meet the Press" on Sunday, two days before a primary in Johnson's home state that Romney hopes will help him to finally lock up the nomination.

"This is nothing negative about the other candidates. It's just a recognition of the fact that Governor Romney has won more delegates. He's the only person that really has a chance to take the winning number of delegates into the convention," said the Wisconsin senator. "We have seven months before the election. Our top priority as fiscal conservatives is to make sure President Obama retires."

There are 42 delegates at stake in Wisconsin, which will vote Tuesday along with Maryland and the District of Columbia. After those April 3 presidential primaries, there will be no more until April 24, when New York, Pennsylvania, Connecticut, Rhode Island and Delaware go to the polls.

Romney is attempting to push the other Republican candidates out of the race as soon as possible, but most of them, particularly former Sen. Rick Santorum (R-Pa.), have said they plan to stay in. Santorum echoed that thought to Chris Wallace on "Fox News Sunday" around the same time that Johnson was making his endorsement.

Johnson said that extending the primary all the way to the Republican National Convention in August would hurt the GOP by keeping the focus off the general election. "It's time to end this so we can spend the next seven months pointing out that President Obama has failed to lead," he said.

Johnson is the 19th senator to endorse Romney, who has received more senatorial endorsements than any other GOP candidate. Last week he picked two big endorsements from Sen. Marco Rubio (R-Fla.), a Tea Party favorite and potential vice presidential pick, and Rep. Paul Ryan (R-Wis.), considered the budget guru of the House Republicans.

On Sunday, Romney almost received the endorsement of the top Senate Republican, Minority Leader Mitch McConnell (Ky.), who stopped just short of officially coming out in support of the candidate.

"I think he's going to be an excellent candidate, and I think that the chances are overwhelming that he will be our nominee," McConnell said on CNN's "State of the Union."

But McConnell said he wouldn't endorse just yet, citing the upcoming primaries in Wisconsin, Maryland and the District of Columbia.

"I'm not sure the voters of Maryland or the District of Columbia need any advice from me," he said.