New York’s non -partisan mayor, the Democrat-turned-Republican who wants to get rid of parties altogether in municipal elections, has discovered his Republican Party roots. On Friday, Mayor Bloomberg finally endorsed the Republican running to unseat the Democratic speaker of the City Council, Gifford Miller, in Manhattan’s 5th Councilmanic District, Jennifer Arangio. The mayor’s intentions had been in doubt ever since the summer, when, on New York One, he said of Mr. Miller, “If he were in my district I’d probably vote for him. I think he’s doing a good job.” Mr. Bloomberg, at the time, seemed to have forgotten the party that gave him a shot at the mayor’s office and whose national convention is set for the city next year. He seems to have regained his wits, but it is still an open question the extent to which Hizzoner will support — as opposed to simply pay lip service to supporting — Ms. Arangio and other Republican candidates for council.

Already, some Democrats are upset that the Republican mayor is starting to act a bit like a Republican. They are charging him with going back on his word last year to support Democrats who did the so-called brave thing by voting with the mayor to institute a 18.5% property tax hike. They’re also feigning belief in the notion that by supporting their Republican opponents the mayor actually is helping the Democrats. This argument is based on the fact that the polls reckon Mr. Bloomberg is as unpopular as Governor Davis of California. But the reason the mayor is so unpopular is precisely be cause he has abandoned Republican principles — by raising taxes and banning cigarettes from restaurants and bars.

It would be nice to think that the mayor’s endorsement of Ms. Arangio will prove to be the first step in a major turnaround. Reeling from the tax revolt that is taking hold in Brooklyn and Staten Island in the wake of his 18.5% property tax increase, Mr. Bloomberg has expressed interest in repealing his fiscal folly. Mr. Miller has indicated that he wants to maintain these high taxes. Ms. Arangio, on the other hand, told the press on Friday about Mr. Bloomberg’s property tax increase that “I would have worked very, very hard to see if there were other alternatives.” So, in a sense, Mr. Bloomberg seems to be moving to repudiate his own past mistakes with this endorsement.

Now Mr. Bloomberg is said to be set to endorse Republican Lisa Giovinazzo, in Staten Island’s 49th Councilmanic District, over Democrat Michael McMahon, who voted for the mayor’s tax hike. These endorsements will be meaningless if they are perfunctory, done with a wink to the Democrats that says “Bear with me.” Given the small number of districts where there are competitive races, the test for the mayor will be whether he risks significant resources — political and monetary — to increasing the size of the three-member Republican minority on the City Council. Better than wasting millions on ad buys to bolster his scheme for non-partisan elections, which he is set to do, would be for Hizzoner to invest some capital in the Republican Party.