House Speaker Nancy Pelosi's delay in sending articles of impeachment to the Senate is "unconstitutional," and the Senate should go ahead and proceed with President Donald Trump's impeachment with or without further cooperation from the House, Harvard Law professor emeritus Alan Dershowitz argues in an opinion piece.

"I believe that the Senate need not wait for articles of impeachment to be transmitted," Dershowitz wrote in the article for The Gatestone Institute. "Senators are empowered by the Constitution to begin a trial now — with or without further action by the House."

"The Senate can make its own rules (as long as they are consistent with the Constitution) and establish its own timetables," he added.

Pelosi's decision to delay transmitting the articles has raised several questions over whether Trump has been impeached, or if the House vote represented an intention to impeach him, with the provision the matter only becomes an "actual impeachment" when the articles are sent.

Dershowitz said the issue is being debated by two of his former Harvard Law School colleagues, professors Laurence Tribe and Noah Feldman, both liberal Democrats supporting Trump's impeachment, but he does not think either one of them is entirely correct.

Tribe believes Trump has been impeached, said Dershowitz, and Democrats will get a "win-win" by refusing to transfer the matter to the Senate. Under this scenario, Trump is impeached but has no opportunity for acquittal by the Senate.

Feldman's opinion is impeachment and a trial go together, and the impeachment vote is the first part of a two-step process mandated by the Constitution. He also says, if the articles are not forwarded to the Senate, that means there has not been a valid impeachment.

Feldman's approach is more consistent with the Constitution, Dershowitz said, but he still disagrees with him.

"My own view is that in the public eye, President Trump has been impeached by a partisan vote and he is now entitled to be acquitted, even if the Senate vote is as partisan as the House vote," he added. "The partisans who voted his impeachment along party lines in the House, have no principled argument against a party-line acquittal."