(Jacquelyn Martin/AP)

This IRS scandal is, as expected, getting most interesting.

People are starting to ask questions about who knew what when — a variant of former Sen. Howard Baker’s famous Watergate hearing question 40 years ago: “What did the president know and when did he know it?”

“I first learned about it,” Obama said on May 13, “from the same news reports [May 10] that I think most people learned about this. I think it was on Friday.”

Which means, except for the acting deputy assistant gardner, he was maybe the last person in the White House to hear about it.

In fact, it sounds increasingly like just about everyone knew about the Treasury Department inspector general’s report, which was released May 14, on the IRS targeting of tea party groups for special scrutiny.

But under the administration’s “Don’t tell Dad” policy, no one bothered to tell Obama or give him even a general briefing before he read about the report in the hated media.

The first White House explanation had it that White House counsel Kathy Ruemmler was given a general heads-up in late April. Then we found out her office knew about it a week earlier. Ruemmler also knew the IG’s findings.

She didn’t tell Obama, but did tell White House chief of staff Denis McDonough. Then an unknown — so far — number of senior White House staff were also clued in. And none of them told Obama -- even, say, a few hours before the media reports.

Now we find that political appointees at the Treasury Department knew a year ago about the IG’s investigation and that Treasury Secretary Jack Lew’s chief of staff, Mark Patterson, discussed the timing of the report with White House deputy chief of staff Mark Childress.

But, under the “Dad” policy, Lew was kept in the dark.

Even if Lew or Obama knew, they hardly would have said anything anyway about the IG report until it became public — lest there be an accusation of interference.

The IG’s heads-up could have given the White House time to put together a seamless, coherent response. Perhaps a few more months’ notice would have helped?