In the wake of his "Nixonian" firing of FBI director James Comey, calls for Congress to begin an impeachment investigation of President Donald Trump have grown.

The Tuesday announcement immediately drew parallels to President Richard Nixon's Saturday Night Massacre, and fueled calls for a special prosecutor or independent commission to investigate alleged Russian interference in the election.

But according to John Bonifaz, co-founder and president of Free Speech For People, there must also be a probe into possible impeachable offenses by the president.

He said the firing Comey

raises serious questions as to whether [Trump] is engaged in obstruction of justice. The FBI director recently testified before Congress, revealing that the FBI is in the midst of investigating potential collusion between the Trump campaign and the Russian Government to interfere in the 2016 presidential election. Members of the House of Representatives must now carry out their constitutional duty and initiate an investigation into whether the President has committed impeachable offenses, including obstruction of justice. Our democracy is at stake.

But as Peter Dreier argues at Salon, that "may have to wait until after November 2018."

That's because "[t]his Republican Congress is not going to impeach Donald Trump," New York Daily News' Shaun King writes. "They are all in so deep with him that impeaching him would be an indictment on themselves."

Or, as historian Kevin M. Kruse puts it:

In sharp contrast [to the House and Senate Nixon faced,] Trump has the extreme luxury of a Republican Congress that has, so far, been reluctant to provide the most basic forms of legislative oversight. Indeed, as we saw this Monday, some senators have contorted themselves into considerable knots to shield this president from any outside inquiry.

Still, two House Democrats see Comey's firing as a catalyzing moment for the movement towards impeachment.

According to The Hill, Reps. Ruben Gallego (D-Ariz.) and Mark Pocan (D-Wis.) laid out that view on a Wednesday call organized by Progressive Change Campaign Committee. The Hill writes:

"We are certainly moving down that path [of impeachment]," said Gallego. "There is a lot of runway until we get there, but the president is not helping himself by firing the person investigating him. … We don't have the numbers to do something right now, but when it comes to a point when we feel there is no other recourse, you'd have—I think—we'd have the full support of the Democratic caucus."

Pocan said that if Democrats had an "impeachment clock" like the "doomsday clock" meant to warn of nuclear war, it would have just moved one hour closer to midnight.

As Dreier sees it, "the unfolding scandal over his Russian ties could eventually lead Trump to follow in Nixon's footsteps" and force him to leave office. "If the Democrats win a majority of seats in the House in November of next year (a real possibility), they will have the power to conduct their own investigation of the Trump-Russia connection, obtain Trump's tax returns to uncover his web of business ties, and begin impeachment proceedings."

But calling for impeachment now "is the appropriate response," writes Ted Glick. "We need to punch back."

Glick, who worked on the Nixon impeachment campaign, adds that "it is the call for impeachment, manifested in all of the various ways it can be put forward, that the people's resistance movement needs to begin integrating into all of our other various issue-oriented and political efforts."

"Impeachment is what the country and the world need," he continues. "Up to now, as bad as Trump has been, that hasn't seemed possible. Now, after Comey's firing, it could be, not right away but over time as the pressure builds."

Bonifaz's organization, along with RootsAction, is leading a national campaign for an impeachment investigation at www.impeachdonaldtrumpnow.org.

Launched on Inauguration Day, the petition says "The President is not above the law," and calls on the House Committee on the Judiciary to investigate possible violations of the Foreign and Domestic Emoluments Clauses "and whether the President has—in violation of his constitutional duty to take care that the laws be faithfully executed—prevented, obstructed, or impeded the administration of justice."

And a new petition from the political action committee Democracy for America also says that Comey's firing adds "another powerful reason for [Trump's] impeachment."

"We have no love lost for Comey, but Trump firing him in order to shut down the Russia investigation is another in a long line of impeachable offenses. This has to stop. Congress must act—NOW," the petition states.