President Obama has been pestered by the birther issue since the 2008 Democratic primary. Why would he wait until yesterday to release his long-form birth certificate and put the issue to rest? Because until now it didn’t make political sense to do so.

Until this spring, birtherism was a political plus for Obama. Let’s face it, screaming for the president’s birth certificate — when there is no evidence he was born outside the country — doesn’t make someone look like the type of person you’d want to hire to walk your dog, much less run the country. By ignoring the question and sometimes laughing it away, Obama came off as cool and reasonable by contrast. His passivity itself was enough to portray birthers as fringe kooks who should not be taken seriously.

In July of 2009, White House Press Secretary Robert Gibbs called the conspiracy theory “made-up, fictional nonsense.” Then the big dismissal: “I almost hate to indulge in such an august setting as the White House.”

Less than two years later, the president thought the issue was important enough to indulge not only in the White House, but personally. It wasn’t the press secretary speaking from the podium yesterday, it was the president himself.

The change can’t be explained by the poll numbers. In the summer of 2009, polls were showing that 25 percent of Americans questioned Obama’s citizenship. Last week, a CBS News poll put the number at 25 percent. What changed the president’s mind, he said, was the media attention.

“But two weeks ago, when the Republican House had put forward a budget that will have huge consequences potentially to the country, and when I gave a speech about my budget and how I felt that we needed to invest in education and infrastructure and making sure that we had a strong safety net for our seniors even as we were closing the deficit, during that entire week, the dominant news story wasn’t about these huge, monumental choices that we’re gonna have to make as a nation, it was about my birth certificate.”

Funny thing about that anecdote. It isn’t true. The birth certificate was not the dominant story. When Washington reporters tweeted that point yesterday, it was suggested that maybe the issue was bigger on cable, and the White House pays too much attention to cable. Maybe. Or maybe the president didn’t want to admit that Donald Trump had gotten under his skin.

If releasing his birth certificate was made necessary because the media were distracted by the issue, and were thereby neglecting the important stories, then why in the world would he release it on the same day news broke of his decision to appoint Gen. David Petraeus as CIA director and Leon Panetta secretary of defense? Surely these are the kinds of substantive stories the media should spend their time covering instead of being distracted by the birth certificate. But with his press conference, the president guaranteed that no one would cover anything that day except the birther issue.

And of course it was a total coincidence that the president happened to hold the press conference at the exact same time Donald Trump was holding a nationally televised press conference in Portsmouth, New Hampshire, on the occasion of his first visit to the first-in-the-nation primary state since 1988.

I don’t buy it. This is a president who doesn’t so much decide to go to war as feel his way to it. He makes emotional decisions. Trump got to him, and the president was going to take him down a notch. If this spring’s birtherism were a sequel to the first time it arose, it would be titled “Birthers II: This time, it’s personal.”

But there’s more to it than Trump getting the hairs on the back of Obama’s neck to stand up. Jerome Corsi’s birther book was soon to be released. To the left, it is an article of faith that John Kerry lost the 2004 election because he didn’t immediately counter the Swift Boaters. He let their story spread until just enough people believed it, and Bush won. Obama decided he wasn’t going to get Swift Boated by the birthers.

So he held his press conference, and the national networks cut to it — and away from Trump — just about the time Trump finished asking why Obama has never released his academic records. Advantage Obama, for now. But something tells me Trump isn’t going to stop asking for those school transcripts anytime soon.