Washington (CNN) " We're in impeachment territory now ," declared David Gergen, the presidential counselor who should know a thing or two about the subject; he advised both a Republican (Richard Nixon) and Democrat (Bill Clinton), who dealt with impeachment in their respective second terms.

Gergen was talking on CNN Tuesday about the revelation that former FBI Director James Comey wrote contemporaneous memos after conversations in which he alleges President Donald Trump tried to get him to drop an investigation into Trump's then-national security adviser Michael Flynn's ties to Russia.

Impeachment, or as Alexander Hamilton called it in the Federalist #65, " a method of national inquest into the conduct of public men," would be a nasty and partisan affair in the current climate.

Take a step back from the whack-a-mole and unending barrage of scandals and missteps that have beset Trump's young presidency, however, and the idea of impeachment, despite growing calls from Democrats ( CNN's KFile has counted 18 Democrats using the "I" word ), seems a long, long way off.

For starters, top Democrats like House Minority Leader Nancy Pelosi and Rep. Adam Schiff, the top Democrat on the House intelligence committee, have not gone there yet. And that's telling. It would take a unified Democratic Party and a groundswell of defecting Republicans to impeach Trump. There's no evidence we're anywhere close to that.

Consider these points, which we've culled from information put out by the Senate and research papers by the Congressional Research Service as well as news reports from 1974 and 1999:

It's a complicated process

Considering how short the document is, the Constitution takes up quite a bit of space on the matter, spelling things out for the House, the Senate and the Executive in Articles I and II.

In Article I, Section 2:

The House of Representatives shall chuse their Speaker and other Officers; and shall have the sole Power of Impeachment.

In Article II, Section 3:

The Senate shall have the sole Power to try all Impeachments. When sitting for that Purpose, they shall be on Oath or Affirmation. When the President of the United States is tried, the Chief Justice shall preside: And no Person shall be convicted without the Concurrence of two thirds of the Members present.

Judgment in Cases of impeachment shall not extend further than to removal from Office, and disqualification to hold and enjoy any Office of honor, Trust or Profit under the United States: but the Party convicted shall nevertheless be liable and subject to Indictment, Trial, Judgment and Punishment, according to Law.

In Article II, Section 4:

The President, Vice President and all civil Officers of the United States, shall be removed from Office on Impeachment for, and Conviction of, Treason, Bribery, or other high Crimes and Misdemeanors.

In plain English, that means first, there needs to be evidence that Trump committed treason, bribery or high crimes and misdemeanors . Not just any crimes and misdemeanors, mind you. High ones. For Clinton, he was accused of perjury and obstruction of justice. For Nixon, list was longer and passed through a House committee as part of three articles. Regardless, it is an extremely broad and subjective target and there's been a lot of scholarship about exactly what it means. So even though this country has historically shown a willingness to give its chief executive a lot of latitude, let's assume this Comey thing (or something else) qualifies. What next?

How would it happen?

The full House would authorize one of its committees, usually the judiciary committee, to investigate and consider impeachment, according to an overview from the Congressional Research Service

That committee conducts an investigation and draws up articles of impeachment.

They then vote in that committee on whether to refer some or all of the articles to the full House.

The Clinton impeachment trial on the Senate floor in Washington D.C. on February 12, 1999. Prompted by the Lewinsky sex scandal, the United States Senate acquitted him on February 12, 1999.

If the committee votes to impeach, they prepare a report for the full House, which then debates and votes on the articles. The House can approve some of the articles and not others. In the case of Bill Clinton, for instance, two of four articles were approved by the full house

If the full House votes for impeachment on a simple majority, the approved articles are then referred to the Senate, which conducts a trial. Chief Justice John Roberts would preside, according to the Constitution. Members of the House lead the prosecution and senators are jurors.

Senators then meet in closed session and vote on whether to convict and remove from office. A conviction requires a two-thirds majority. That's 67 senators. Sixty-seven!

Republicans control the House and Senate

Both Nixon, who wasn't actually impeached, and Clinton, who was impeached by the House but acquitted by the Senate, were facing off against a hostile Congress controlled by the opposing party. So was Andrew Johnson, the Democratic vice president who succeeded Abraham Lincoln as president after his assassination and was impeached by the hostile Republicans who controlled Capitol Hill. He was acquitted too. Got that? the Senate is 0-for-2 on convicting presidents from the other political party.

Republicans -- Trump is a Republican, remember -- have a 238-193 majority in the House. That means 20 or more Republicans, depending on who is voting, would have to break ranks to impeach their Republican President.

And that would be the easy part.

Republicans currently have 52 senators, so 19 of them would have to break ranks and vote to convict a Republican president, assuming all Democrats voted to do so.

Nixon, by the way, resigned before impeachment went to a vote in the full House of Representatives. In that case, most of the Republicans on the judiciary committee opposed the articles.

Republicans have not turned on Trump

There is not even a critical mass of Republicans who think there should be a special prosecutor to investigate the Trump campaign's ties to Russia. Exactly zero Republicans have said anything close to supportive of impeachment. Trump is likely to be protected by his Republican allies.

Impeachment is extremely rare

Just 19 people -- two presidents, one senator, one secretary of war and 15 judges -- have been impeached by the House and tried in the Senate. Of those, only eight were convicted. Seven, including both impeached presidents, were acquitted. Charges were dropped against three others after they were either expelled from office or resigned.

Most officials who get to the point of impeachment would rather resign a la Nixon than face a public trial in the Senate. The US also has regular elections. A representative or senator is more likely to be expelled from their respective body by their peers or kept from re-election by the voters.

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It takes a long time

The impeachment process takes months and months. There are years of this administration in front of us, but the impeachment process would seem like an eternity in the Trump era if the current pace of news keeps up. The House first voted to consider impeaching Nixon in February 1974. The House judiciary committee didn't vote on an article of impeachment until July 24. Nixon resigned on August 8 of that year before the full House had voted.

Clinton was acquitted by the Senate, although a majority voted against him, on February 13, 1999