Cummings, a Maryland Democrat, issued the subpoena in April to Mazars USA, an accountant for the president and Trump Organization. The question for the judge overseeing the case, Amit Mehta, is whether the House's subpoena is a valid exercise of legislative power. Mehta was nominated to his position by President Barack Obama.
In asking the judge to block the subpoena, Trump in essence asked the judicial branch to stop the legislative branch from investigating his past. Decades of precedent has established that the legislature's investigative power is not limited to just researching possible legislation.
The lawsuit comes amid a widespread effort by the White House and the president's attorneys to refuse to cooperate with congressional requests for information and records.