The first round of the District’s 2015 budget approval process could have been billed as the lame-duck mayor vs. the D.C. Council. But that shorthand would downplay what appeared to be the beginning of the muscular reconstruction of Phil Mendelson’s chairmanship of the council.

Mendelson (D) became the city’s legislative leader almost by accident, or at least through misadventure: Kwame Brown (D) resigned as chairman after being charged with felony bank fraud in 2012; the remaining council members chose Mendelson, an at-large member, as the interim replacement. But he decided he wanted to stay there. He won a special election for the seat in 2012 and, after triumphing in the Democratic primary this April, appears poised to claim a full four-year term as chairman in November’s general election.

Could that prospect be the reason behind the new, emboldened chairman on display last week? Or is the robust Mendelson an apparition?

“It seems he’s starting to find his footing,” said longtime civic activist Terry Lynch.

I have lambasted Mendelson for his failure to lead, drawing attention to his often bland, namby-pamby approach and the fact that some of his colleagues have jokingly called him “staffer Phil.” The nickname acknowledges his approach to governance: all trees, no forest.

Equally troubling, as the government — and the city’s image — slid into a ditch last year after details about the corruption surrounding Mayor Vincent C. Gray’s 2010 campaign became public, Mendelson didn’t step up to attempt a rescue. Some council members called for the mayor’s resignation. Mendelson was mostly mum, arguing only that the legislature had to restore the public’s trust. Duh.

Residents began to lament the absence of strong council leadership. The level of apathy within the city rose exponentially. No one should have been surprised when only about 27 percent of registered voters showed up at the April 1 primary.

However, a new Mendelson appeared to have reported for duty last week. During the first phase of the budget-approval process, he snatched money from the streetcar project, aggressively pushed through a historic package of tax reforms and effectively beat back an effort by veteran council members Jim Graham (D-Ward 1) and Marion Barry (D-Ward 8) to strip money from a welfare training program. That last move would have delayed, yet again, implementation of the legal mandate to remove from the program recipients who have been in it for five years or more. (A similar federal requirement went into effect in the mid-1990s. But the District — a haven for bleeding-heart liberals — moved to take such action only in recent years, setting a graduated scale for ending welfare services and participation.)

Mendelson said he merely listened to his colleagues and knew what they would support: “I’m not on my own.”

It’s true the majority of council members got in line behind him, but Mendelson’s demeanor on the dais was tough and confident. “It’s a sea change. It’s part of Phil’s maturation as chairman,” said Lynch.

Of course, not everyone agrees: Dorothy Brizill, executive director of DCWatch, a good-government group, said, “Phil doesn’t have that leadership gene. The best I can say is that he has learned a new math. He’s learned how to count” to seven, the number of votes necessary to get legislation approved by the 13-member council.

It’s more than that, however. Consider that Mendelson sued Gray, Chief Financial Officer Jeffrey DeWitt and Attorney General Irvin B. Nathan after the District’s executive branch announced that it would not honor the voter-approved budget autonomy law. Mendelson lost the case but demonstrated his willingness to rumble with the mayor, who is perceived as a political ally.

Passage of the tax reform package was yet another example. In his 2015 budget, Gray had proposed implementing only a few of the recommendations by former mayor Anthony A. Williams’s tax commission. The council, led by Mendelson, went much farther. Its decision to impose a sales levy on previously untaxed services such as fitness club memberships and yoga classes drew sharp rebukes from the businesses and residents.

Mendelson told me that he doesn’t intend to buckle under the pressure. In the past, he probably would have been trying to forge a compromise.

Compliments certainly are deserved. But, truth be told, the jury is still out on whether Mendelson has decided to fully accept the leadership role demanded of the council chairman or whether he is, indeed, exploiting the weakness of a lame-duck mayor.