Powerful House Democrats are about to blitz the Trump administration with subpoenas and investigations. Pay attention to their nonprofit helpers, many of which are new.

For nearly a decade, the left has decried the Supreme Court’s Citizens United decision, which restored speech freedoms and enabled hundreds of tea-party groups. For just as long, they have bitterly criticized conservative watchdogs such as Judicial Watch, which they accuse of using litigation to hound the Obama administration. Various liberals have called Judicial...