For the third time in almost 46 years, the House of Representatives has voted to begin a formal impeachment inquiry into the actions of the sitting president.

And despite criticisms from President Trump — whose press secretary Stephanie Grisham called the resolution "unfair, unconstitutional, and fundamentally un-American" — the measure lawmakers approved Thursday charts a course similar to that of the inquiries into Presidents Richard Nixon and Bill Clinton.

The process allows for the investigation led by House Intelligence Committee Chairman Adam Schiff, D-Calif., to continue, with the next phase including public hearings. Up till now, most of the investigation has been closed-door depositions, involving Democrats and Republicans on three House panels — intelligence, oversight and foreign affairs.

"The process seems very fair to me," said former Republican Rep. Tom Campbell, who served in the House during the Clinton proceedings and voted for impeachment. He called the current plan "very consistent with how the House operates in the two previous impeachment matters."

Due process

Trump and Republican allies argue that he and the GOP do not have enough power in the proceedings. White House press secretary Grisham said that with Thursday's vote,"Speaker [Nancy] Pelosi and the Democrats have done nothing more than enshrine unacceptable violations of due process into House rules."

Republican lawmakers have been allowed equal time for questioning in the closed-door depositions. They will be allowed to request subpoenas and witnesses for the open hearings, but those would have to be approved by the Democrats.

Schiff will eventually turn his findings over to the House Judiciary Committee, which would begin the formal process of determining whether to draw up articles of impeachment.

House Judiciary Chairman Jerry Nadler, D-N.Y., has laid out additional details about the minority party's role for his panel.

The president or his attorneys will be allowed to cross-examine witness and subpoena their own, although they'll need a majority vote or the concurrence of the chair to do so. They will also be allowed to attend all hearings of the Judiciary Committee, including any that are closed to the public.

Democrats say that these same rights were given to the minority party with Clinton in the late 1990s and Nixon in the mid-1970s.

The resolution also says that if the president "unlawfully refuses to cooperate with Congressional requests," Nadler can deny requests by the president or his counsel, an apparent attempt to counter Trump's lack of cooperation with requests for documents and witnesses.

Too secretive?

Another talking point for Republicans is that the investigation has been largely hidden from public view.

"It is, by any definition, a process that is an attempt in secret, in the basement of the Capitol, to unseat a duly elected president of the United States," said House Republican Conference Chair Liz Cheney on Thursday. "It's unlike anything we've ever seen before."

But both the Clinton and Nixon investigations had a mix of closed and open phases.

Independent counsel Kenneth Starr's investigation into Clinton also used closed-door interviews and grand jury proceedings that were not open to Congress until later.

The Nixon investigation was a bit different. It started out as investigation into the Watergate break-in, noted Thomas Alan Schwartz, a professor of history and political science at Vanderbilt University.

"So there were, of course, the very famous Watergate hearings in the summer of '73 that went on at great length that were sort of a national obsession," he said. "And the question, you know the famous Howard Baker question: 'What did the president know and when did he know it?' "

After the Watergate hearings ended, though, the Judiciary Committee also conducted several closed-door hearings as it proceeded with impeachment.

Key differences

Campbell, who now teaches law at Chapman University, says one difference between the process this time and when Clinton was impeached was the information lawmakers had.

In 1998, he says, House members voted to authorize an impeachment inquiry only after they received the Starr report. Starr investigated, among other things, whether Clinton lied about the affair he had with White House intern Monica Lewinsky.

"So in that sense," Campbell said, "every member of the House had available to her or him the findings of this special prosecutor. Now, in this case, that's not so — unless one refers to Robert Mueller's report."

Another difference, looking back to the Watergate era, is the political climate.

"This president retains a very strong support within his party in a way that Richard Nixon really lost or did not have that same degree of loyalty," professor Schwartz says. "He also has a media platform that Nixon did not have — the media environment was very different."

The bipartisan nature of the Nixon impeachment inquiry had evaporated by the time Clinton was impeached.

Michigan Democrat John Conyers argued against impeaching Clinton on the House floor at the time, saying, "I am witnessing the most tragic event of my career in the Congress — in effect, a Republican coup d'etat in process."

The era of partisanship and polarization present then is still very much present today, as evidenced by Grisham's charge that "the Democrats are choosing every day to waste time on a sham impeachment — a blatantly partisan attempt to destroy the President."

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