SAN ANTONIO — Last year, in deciding against a statewide run for comptroller, state Rep. Mike Villarreal cited a well-worn maxim.

“Timing is everything in politics,” he said.

Now, Villarreal, D-San Antonio, feels the time is ripe to run for mayor in 2015.

And he's wasting no time in declaring it.

The longtime state representative started seeking support from community leaders days after news broke on Saturday that Mayor Julián Castro likely is headed for Washington to join the Cabinet of President Barack Obama.

The president is expected to nominate Castro as his new secretary of housing and urban development, and Castro has signaled a willingness to accept.

“I think it is a significant challenge that we are facing if we lose Julián Castro,” Villarreal told me. “And if we do, then I feel like I want to come home and focus my energies and attention in serving my city as mayor of San Antonio.”

Villarreal, 42, has served in the Legislature nearly 15 years.

The Harvard graduate is known for digging into budgets and crunching numbers to support progressive stances, with education funding a regular focus. The crux of his new campaign, he said, is education.

“My core mission is to make San Antonio the greatest place to raise children healthy and ready for the future,” Villarreal said. “And that's not just a policy statement for me. That's a personal motivation. I'm raising my kids here and I want them to raise their kids here.”

In campaigning for a nonpartisan post, Villarreal is fashioning himself as a “consensus builder,” a Democrat who has ably navigated a Republican-ruled state Capitol.

He called House Speaker Joe Straus, R-San Antonio, a “close friend and ally.” And he acknowledged a former alliance with state Rep. Tom Craddick, R-Midland, when the latter ruled as House Speaker.

“The way I want to run for office is how I want to govern,” Villarreal said, “and that is I'm building a coalition of Republicans and Democrats, North Siders, South Siders, folks who live on the East Side and the West Side, to support me in this effort.

“It is going to be a reflection of our city,” he continued. “And that's the way it should be. And as I call people who are as diverse as leaders in our chamber of commerce to leaders in West Side grass-roots organizations, they tell me, 'I am so happy.'”

As a would-be bridge builder, though, Villarreal is touting the same strengths as another mayoral candidate: District 8 Councilman Ron Nirenberg, who leads a North Side district that's a mix of Democrats and Republicans.

And Villarreal's House district overlaps with the turf of another likely opponent: District 1 Councilman Diego Bernal, who is “seriously considering” a mayoral run next year. District 6 Councilman Ray Lopez is another mayoral hopeful who would fight for the same votes as Villarreal.

In short, he's already facing an array of competitors.

That was clear Tuesday night at the home of Ed Whitacre, former chairman and CEO of General Motors and AT&T.

Whitacre was holding a fundraiser for County Judge Nelson Wolff, and the county judge's son, Commissioner Kevin Wolff, noted the politicking presence of the four front-runners: Nirenberg, Lopez, Bernal and Villarreal.

The latter “did call me a couple days ago,” Kevin Wolff said. “To his credit, he was very direct and asked if I was with him. I told him, 'Mike, it's a little early. Let's see how some of these things fall out first.'”

On the topic of timing, Villarreal now must decide how to contend with his own obligations as a legislator.

He's running unopposed in his own district in November, and he told me he won't resign his seat before the election. The next legislative session begins in January and runs through May.

That means Villarreal could face the political paradox of campaigning for mayor in San Antonio while serving his district in Austin.

What he plans to do about this, he said, remains a “question mark.”

In a city in sudden flux, it's one of many.