Throughout his Hall of Fame baseball career, Jim Bunning was famous for the brush back pitch: a fastball inside to a batter crowding the plate. Now Mr. Bunning, a Republican from Kentucky who is retiring after this year, is throwing a political brush back in the Senate on behalf of fiscal responsibility.

And all hell has broken loose. Mr. Bunning has dared to put a hold on a $10 billion spending bill to extend jobless insurance and fund transportation projects. Mr. Bunning says he won't yield until the Senate finds a way to pay for the new spending with cuts somewhere else in the $3.5 trillion budget. For this perfectly reasonable stance, Mr. Bunning has become the Beltway and media villain of the hour. We'd call it his finest hour.

Every time Washington wants to spend money, the Senate Majority Leader asks for "unanimous consent" to authorize the funding, and in the collegial Senate everyone falls in line. But when Harry Reid wanted consent last week for that $10 billion, Mr. Bunning broke the old-boy rules by shouting: "I object."

The faux indignation has been something to behold. "It is simply unfair for one Senator to attempt to hold the Senate hostage," said Senator Richard Durbin. "Unfair," cried Jay Rockefeller. The Obama Administration has attacked Mr. Bunning for playing "political games" and forcing a furlough of 2,000 government workers. (The horror!)

By the way, Democrats could end Mr. Bunning's stand by invoking cloture and getting the 60 votes they need to proceed. Mr. Reid won't do that because he thinks he's scoring points using Mr. Bunning to define Republicans as "obstructionists." So who's playing politics here?

Mr. Bunning is merely asking the Senate to live by the rules that President Obama said it should when he signed an executive order requiring "pay-as-you-go" budgeting. "Now, Congress will have to pay for what it spends, just like everybody else," he said, only three weeks ago. But instead of backing Mr. Bunning's stand that new spending must be "paid for," the White House is attacking him.

The real story here is that Mr. Bunning is exposing pay-go as a fraud. When Mr. Obama and Democrats want to spend money on their priorities, they waive the rule by declaring an emergency. They only enforce pay-go to block tax cuts. The Senate will soon follow with another $85 billion spending bill, and rest assured that too will violate pay-go rules.

Another truth is that Mr. Bunning is making most Republicans as uncomfortable as he is Democrats. Bob Corker of Tennessee and Jim DeMint of South Carolina have stood up for him. But most Republicans were content to obey Mr. Reid's request to borrow $10 billion more, and they find Mr. Bunning embarrassing. As we went to press last night, the pressure on Mr. Bunning to give way was intense.

Susan Collins of Maine asked him to stand down and told reporters that his "views do not represent a majority of the Republican caucus." Ms. Collins wants a return to budgeting as usual. But business as usual has the U.S. government running a $1.4 trillion deficit, and it's about time someone stood up for taxpayers.