The resolution filed Wednesday by Rep. Brad Sherman, D-Calif., is largely identical to a draft Sherman floated last month — one that accuses Trump of obstructing justice by "threatening, and then terminating" former FBI Director James B. Comey and includes language lifted from the impeachment charges against President Richard M. Nixon.

The four-page resolution, H.Res.438, garnered a single co-sponsor upon introduction: Rep. Al Green, D-Texas, who has also been an outspoken proponent of impeachment proceedings against Trump but has not filed a resolution of his own.

The filing of an impeachment resolution against a president in itself is not terribly uncommon. Since Nixon, individual members of Congress have sought the impeachment of presidents Ronald Reagan, Bill Clinton and George W. Bush. What is much more serious is the launch of a formal inquiry by the House Judiciary Committee, and the subsequent adoption of impeachment articles by the House, resulting in a Senate trial.

In an interview Wednesday, Sherman said his decision to file the resolution Tuesday has been driven by the House calendar and the timing of his own review process — not by the revelation Tuesday that Trump's son accepted a meeting with a lawyer tied to the Russian government with the understanding that the lawyer might have information damaging to Democratic presidential candidate Hillary Clinton to share.

But, Sherman said, the emails released by Donald Trump Jr. "add credibility" to the notion that Trump fired Comey in order to derail the federal investigation — one that now appears certain to envelop his son.

"Clearly you can no longer say that collusion is an unsubstantiated fantasy of crazy leftists," Sherman said.

But it remains fantastic to think that the impeachment push might proceed in any meaningful way in the coming months. Highlighting that reality is the lack of Democratic support for the push, let alone backing from Republicans. House Minority Leader Nancy Pelosi, D-Calif., has called for the completion of the pending investigations by congressional committees and by Special Counsel Robert Mueller before entertaining the notion.

Green said Wednesday that he signed on "to see how the House responds" and reserved the right to file impeachment articles of his own.

Two other key Democrats said Wednesday they had doubts about Sherman's push.

California Rep. Adam Schiff, the top Democrat on the House Permanent Select Committee on Intelligence, which is probing Trump's Russia ties, said he was "keeping my focus on following the facts."

"From my point of view, it's far too early to be thinking about where the investigation will conclude," he said.

And Rep. Jamie Raskin, D-Md., a law professor who sits on the House Judiciary Committee and has talked since January about the likelihood of a Trump impeachment, said he was surprised by Sherman's move. He said he would review the resolution but might not sign on.

"Impeachment is a mixed question of law, facts, and politics," said Raskin. "The law and the facts are beginning to crystallize, but the politics are just not there yet without Republicans willing to break from partisan discipline."

Sherman downplayed the lack of support from his Democratic colleagues, and he said the next step was to convince the Republican-controlled Judiciary Committee to hold hearings.

"It's always nice to have co-sponsors," he said. "But I don't think that's the key thing here. The key thing is to get the ball rolling."