With Trump Impeachment Calls Growing, the Definitive Guide to Removing a President Has Been Published Online

With President Donald Trump besieged by allegations and revelations regarding his and his 2016 campaign's links to Russia, the key chapter of the definitive volume on impeachment has been published online in its entirety for the first time.

Related: Trump impeachment calls surge as president faces 'most serious scandal' in U.S. history

Charles Black Jr.'s Impeachment: A Handbook was first published in 1974 during the Watergate crisis that would lead to the resignation of President Richard Nixon before his probable impeachment. In 1998 it was reissued, shortly before President Bill Clinton was impeached by the House of Representatives (only to be saved by the Senate, which acquitted him). Now, with impeachment talk once again swirling, the Lawfare blog has posted what Black termed the "heart of the matter."

For those who have been rushing to break out the "I" word, including one Democrat who has already filed an article of impeachment in the House, Black's words provide a note of caution and an instruction to use methodical reasoning rather than partisan passion.

"We may justifiably hope that those who have to make this political judgment will see it as high-political, and not as having any connection with partisan politics, or with views on policy," Black writes.

Elsewhere, he states, "General lowness and shabbiness ought not to be enough. The people take some chances when they elect a man to the presidency, and I think this is one of them."

Representative Brad Sherman (D-Calif.) first began the process earlier this month, introducing an article of impeachment against Trump that accuses the president of obstruction of justice.

Trump is reportedly being investigated for possible obstruction of justice by special counsel Robert Mueller, following former FBI Director James Comey's testimony that the president asked him to ease up on an investigation into his former national security adviser, Michael Flynn, before he was fired by Trump.

Obstruction of justice was one of the charges both Nixon and Clinton faced. It has generally been perceived as falling under the "high crimes and misdemeanors" section of the three grounds for constitutional impeachment, which also include treason and bribery.

Black argues that the authors of the Constitution did not intend for all obstruction of justice offenses to be impeachable. Instead, he says, the offense should be related to "public affairs and the political system."

He adds, "But the obstruction of justice is ordinarily a wrong as well as a crime, and when it occurs in connection with governmental matters, and when its perpetrator is the person principally charged with taking care that the laws be faithfully executed, there must come a point at which excuses fail."

While some have been increasingly happy to talk up the prospect of Trump being removed from office, Democratic Party leaders have generally taken a more cautious approach.

"I've been asked questions: Is this collusion? Do you have evidence of collusion? Right now, no," the Senate Judiciary Committee's top Democrat, Dianne Feinstein, said last month. "Not what I would call sufficient. Suspicion is one thing, evidence is another."

It is a message Black shares. "The concreteness of the evidentiary case is all important," he writes.

But as for Black's urging that impeachment should not be a partisan issue, that is likely, one way or another, to fall on deaf ears.

Even those calling for impeachment acknowledge that it is ultimately a political decision and is almost a lost cause while the Republican Party controls both the House and the Senate. To impeach a president, a majority vote is required in the House and a two-thirds majority in the Senate.