John McCain may interrupt his campaigning to return to Washington in an effort to pass a one-year moratorium on earmarking. The Hill reports that McCain’s return puts the rest of the Senate GOP caucus in a tough position. Do they show unanimity with the party’s nominee, or do they protect their ability to protect their incumbencies?

Sen. John McCain (Ariz.) may return to Capitol Hill this month to support an amendment imposing a one-year ban on earmarks, a move that could set up a divisive clash within the GOP caucus.

McCain, the likely Republican presidential nominee, has long broken with most of Congress, including the Senate Republican leadership, in seeking an end to the practice of inserting line items in spending bills for parochial projects.

His return could set up a clash with many Senate Republicans who argue that it is the prerogative of Congress to set spending priorities, and earmarks are acceptable so long as the process is transparent. Earmarks take on added importance in an election year because lawmakers often point to the projects to tout their effectiveness in Congress.

McCain has tried to convince his colleagues to eschew earmarks for years, and now he may have them exactly where he wants them. As the party’s nominee, he has the power of the media spotlight, and he has not hesitated to use that leverage in the past to twist arms. He also has the high road on this issue; it’s a lot easier to say that pork is corrupting Congress than it is to explain how earmarking somehow retains accountability over procurement.

Senate Republicans now face the same choice that House Republicans blew at their annual retreat. They have an opportunity to send a clear message on clean government. A one-year moratorium on earmarking would show voters a commitment to changing the environment and the processes in the Beltway that has brought sclerosis to the electoral process. It would reject the Treasury raids for incumbency protection — and any pushback by the Democrats would enhance the GOP brand for 2008.

McCain can’t lose in any sense. If he and DeMint can’t budge the Senate, he will enhance his general-election image as a maverick, a man who can challenge his party. If the amendment passes, McCain will enhance his argument that he and not Barack Obama is the real agent of change. The only question will be whether the Republicans choose to be winners or losers.