There is absolutely nothing in the Constitution or congressional rules that requires the House to take a formal vote before commencing an impeachment inquiry. 

But lawmakers should do it anyway.

The demand for a vote has become a favorite Republican talking point.

"Your inquiry is constitutionally invalid and a violation of due process," White House counsel Pat Cipollone wrote in an embarrassingly unprofessional and histrionic letter to House Democratic leaders. "In the history of our Nation, the House of Representatives has never attempted to launch an impeachment inquiry against the President without a majority of the House taking political accountability for that decision by voting to authorize such a dramatic constitutional step."

Trump is not being denied due process, or even simple fairness. An impeachment proceeding in the House is a fact-finding endeavor, similar in many respects to a grand jury proceeding. The trial, if there is to be one, would take place in the Senate. And Article I of the Constitution could hardly be clearer that the House has the "sole power" of impeachment, which includes the ability to decide just how it wants to go about it.

Still, putting the authorization of an impeachment inquiry to a vote − something Speaker Nancy Pelosi, D-Calif., has declined to do thus far, but has not ruled out − would set the House on higher moral ground, with little political downside.

There is no question it would pass, given that 227 House Democrats and 1 independent have already announced their support for an inquiry, which is 10 more votes than needed. And it is not outside the realm of possibility that a few brave Republicans might join them, given that each day lately brings a new set of revelations of shockingly abusive conduct on the president's part.

By offering this concession, House Democrats would expose the White House's stonewalling for what it is, and put Republicans in an uncomfortable spot. They would have to go on record with an answer to the question that many of them have been ducking: Do they see anything worth investigating in the behavior of a president who has acknowledged leaning on the Ukrainian president to dig up dirt on a presidential rival, and has asked the Chinese to do the same?

A vote could also strengthen the Democrats' hand in court, which is where much of this clash between the legislative and executive branches appears to be headed.

We saw a hint of that Tuesday, at a hearing on the House Judiciary Committee's lawsuit to obtain grand jury materials gathered in special counsel Robert Mueller's Russia investigation. The issue at hand is a technical argument over whether the lawsuit is "preliminary to or in connection with a judicial proceeding," which means it would qualify for an exemption from grand jury secrecy rules.

Chief U.S. District Judge Beryl Howell asked House general counsel Douglas Letter: "Wouldn't it make your request for grand jury material a lot easier if the House would have taken a vote authorizing an impeachment inquiry? Easier for all of us?"

Letter conceded: "Right. I could sit down . . . you probably would rule on this immediately. I could sit down, and we'd be done."

Bringing the impeachment inquiry to a vote on the House floor would open up arguments on other questions. House Minority Leader Kevin McCarthy, R-Calif., has demanded that the Democratic chairman and Republican ranking member of each committee involved should have "co-equal subpoena power," which the GOP members would no doubt use to turn the whole thing into a circus.

But there is an easy answer to that one, as well. The House already has procedures in place for subpoenaing witnesses and material − procedures that the Republicans themselves engineered to put the minority at a disadvantage back when they controlled the House. In 2015, possibly anticipating a Hillary Clinton presidency, the House's GOP majority vastly expanded the ability of chairmen to issue subpoenas unilaterally, without consulting the ranking member or the rest of the panel.

What House Democrats should not do, however, is commit to keeping the impeachment inquiry narrowly defined to Trump's now-infamous phone call with Ukraine President Volodymyr Zelensky, which prompted the whistleblower report that got this whole investigation rolling. We are learning that this blatantly improper act was a symptom of a much more virulent and metastatic pathology infecting the presidency. Congress should take its time, and explore how far it has spread.

Karen Tumulty is a political columnist at The Washington Post.