One of the leading liberal lights of American law now says the “IRS is engaged in unconstitutional discrimination against conservative groups and must be halted.”

To be clear, Harvard prof Laurence Tribe is a convert: Early in the week, he sent out a tweet dismissing the idea of an IRS scandal as long-debunked.

But, as the Cato Institute’s Walter Olson noted at Overlawyered, for once social media actually shed light on a dispute: Others asked Tribe to read this month’s DC Circuit Court of Appeals ruling against the IRS in the case — and he did.

That unanimous decision, reinstating lawsuits against the IRS for its targeting of righty groups, noted that there’s “little factual dispute” about the targeting and the “unequal treatment” of conservatives. More, it’s “plain . . . the IRS cannot defend its discriminatory conduct on the merits.”

Tribe read that, plus a key Inspector General report, and tweeted, “I confess error [with regard to] IRS ideological targeting. The IG report and the [DC Circuit] decision seems right to me. Inexcusable abuse.”

If a liberal icon can see the serious abuse, there’s hope for the House drive to impeach IRS chief John Koskinen for his scorched-earth defense of the cancer in his agency.