Peter Bergen is CNN's national security analyst, a vice president at New America and a professor of practice at Arizona State University. He is completing a book about President Trump's national security team and policies. The opinions expressed in this commentary are his own. View more opinion articles at CNN.

(CNN)The whistleblower complaint, taken together with the transcript of President Trump's July 25 call with Ukrainian President Volodymyr Zelensky that was released earlier this week by the White House, explain why Nancy Pelosi is finally getting behind impeachment proceedings: A sitting president appears to have abused his office for political gain, and White House officials allegedly engaged in a cover-up of that effort.

Impeachment proceedings went ahead against President Richard Nixon because he engaged in a cover-up of a break-in at the Democratic Party office at the Watergate, of which he claimed to have no advance knowledge.

Intelligence community watchdog feared Trump's Ukraine call was 'national security' risk

As is so often the case in Washington, it was the cover-up that rose to the level of a breach of public trust that was the grounds for impeachment proceedings against Nixon.

In Trump's case, Democrats in the House can credibly make the case that while in office Trump pressured a foreign leader to dig up dirt on a political opponent, Joe Biden, and his family. President Trump insists he did nothing wrong.

And then Trump officials, realizing that there was something unseemly about the call between Trump and the Ukrainian President made every effort, according to the whistleblower, to "lock down" the transcript of the call by removing the transcript from where these transcripts are generally stored and loading it on a separate computer system where only the most classified and sensitive communications are stored, despite the fact that there was no classified information in the call.

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The United States has had an interest in supporting Ukraine's sovereignty -- in particular since Vladimir Putin seized Crimea, a part of Ukraine in 2014 -- and continues to support rebels in the eastern half of the country. That US support includes nearly $400 million of military aid that Trump put on hold just before his call with the Ukrainian President.

What is striking is the tone of the whistleblower's complaint: This is a savvy Washington bureaucrat. This person is quite familiar with the law as it applies to whistleblowers and savvy enough to have presented his/her complaint at an unclassified level (with some classified material in an appendix) so that when it publicly surfaced, as it did Thursday morning, the public could make its own judgments about the nature of the whistleblower's complaints against President Trump and his enablers.