Keeping a campaign promise is a worthy purpose — unless the promise was a mistake in the first place. So it is with the Democratic leadership’s decision to cancel Members’ cost-of-living adjustments this year because the federal minimum wage hasn’t been increased.

Cancellation of the scheduled 1.7 percent COLA was written into the huge continuing resolution passed in December at the close of the 109th Congress and reaffirmed in the joint funding resolution just laid down by Senate Appropriations Chairman Robert Byrd (D-W.Va.) and his House counterpart, Rep. David Obey (D-Wis.).

Republicans are objecting — legitimately — to the injection of Congressional pay into last year’s election campaign, arguing that it violates an eight-year understanding that the parties should not attack each other over pay raises. At the same time, it was the Republicans’ utter failure to fund the government in an orderly way that created the opportunity to cancel the COLA.

The principle here is that Members of Congress earn their pay and deserve to receive an annual increase regardless of what laws they pass or don’t pass. The scheduled pay level for rank-and-file Members, $168,500, is hardly excessive for government executives doing full-time work, and most Members could be earning much more in the private sector.

Congressional pay once was a perennial political football until both parties agreed to stop kicking it around and establish an annual COLA that could be canceled only by a specific act of Congress. Every year, efforts are made on one ground or another to cancel it. In October 2005, for instance, the Senate passed a COLA-cancellation measure by a vote of 92-6, with proponents arguing that the money involved (all of $2 million) should be spent on Hurricane Katrina recovery.

Tying Congressional pay to the federal minimum wage perhaps has the merit of germaneness — both involve pay — but this is a precedent that will be repeated and possibly extended. No one has argued — yet — that Members’ health benefits should be tied to availability of adequate coverage for the uninsured, but the door certainly has been kicked ajar. For sure, COLAs will be back in play as a football every year from now on.

Fortunately, the Byrd-Obey funding resolution does contain $41 million in additional funds that can be used for Congressional staff COLAs at the discretion of Members. We trust most will award it to staffers and not make them suffer because of a political play by their bosses.

Republicans also are complaining about the fact that Byrd and Obey produced a 137-page document to finance the government through this fiscal year, not a simple continuing resolution. It’s a hollow complaint after the GOP passed only two out of 12 appropriations bills last year, leaving a mess for Democrats to fix.