How can one tell an issue has truly arrived? Politicians rush to prove themselves authentic on it. That appears to have happened with the pork moratorium proposed by Senator Jim DeMint (R-SC), as all three Senators still running for President have now agreed to co-sponsor his resolution:

Obama joined with other lawmakers last year to obtain almost $100 million worth of earmarks for Illinois. Clinton worked with others to win $342 million in pet projects for New York and Pelosi obtained $94 million for California.

“We can no longer accept a process that doles out earmarks based on a member of Congress’ seniority, rather than the merit of the project,” Obama said in a statement. “We can no longer accept an earmarks process that has become so complicated to navigate that a municipality or non-profit group has to hire high-priced D.C. lobbyists to do it.”

McCain, the Republican presidential nominee-in-waiting, has fought — and lost — many battles over earmarks before, but his new status has longtime rivals in his own party rethinking their positions.

The moves by Clinton and Obama have also put Senate Majority Leader Harry Reid and other Democrats in a quandary. Reid issued a statement early Monday reiterating his support for Congress’ right to direct money back home for roads and other projects.

McCain is among only six members of the Senate who don’t ask for pet projects. Obama does, though his requests are generally modest when compared to more senior senators like Illinois colleague Dick Durbin, a fellow Democrat.

What does this tell us? It says that the outcry over the incumbency protection of pork has finally made it a political liability. John McCain’s credibility on the issue creates a problem for Barack Obama and Hillary Clinton. Both of the Democrats have used earmarks to build their political strength. Both of them need to be seen as reformers, Obama because he’s running explicitly as a reformer and Clinton to keep up with Obama.

But will this mean success? I suspect not. John McCain has fought pork for his entire career, and he still only has a handful of Republicans with him on the policy. Hillary and Obama have less standing and even fewer colleagues looking to end pork-barrel politics. Their co-sponsorship allows them to look good on pork without any real risk, as a coalition of Democrats and Republicans will almost certainly vote to defeat DeMint’s amendment.

Still, even if this happens, their sudden need to look kosher on pork shows that the issue has gained significant traction. At first the Beltway laughed at Porkbusters, then ignored them, and then opposed them. Eventually, they will have to come to a reckoning on the corrupting and wasteful influence of pork. Hopefully, the DeMint amendment will provide that opportunity, but it now looks inevitable in one form or another.