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Why are House Democrats stonewalling questions about the identity of the Trump-Ukraine whistleblower?

Start by taking them at their word. Perhaps they really are concerned about the whistleblower's personal safety. They also know that, beyond a limited prohibition applying only to the inspector general of the intelligence community, no law bars anyone -- in politics, media or anywhere else -- from revealing the whistleblower's identity. So they worry.

But there is more to the story. Should the whistleblower have connections to prominent Democrats, exposure of his identity could be embarrassing to the party. And perhaps most of all, reading through the impeachment inquiry depositions that have been released so far, it's clear that cutting off questions that could possibly relate to the whistleblower has also allowed Democrats to shut off any look at how the Trump-Ukraine investigation started.

Who was involved? What actions did they take? Why did some government employees think President Trump's July 25 call to Ukrainian President Volodymyr Zelensky represented a lost opportunity, or poor judgment, while others thought it represented wrongdoing requiring congressional investigation?

Democrats do not want the public to know. And that is a position familiar to anyone who has watched Washington for the last two years: The Democrats' determination to cut off questions about the origins of the Trump-Ukraine investigation is strikingly similar to their determination to cut off questions about the origins of the Trump-Russia investigation. In both cases, they fought hard to keep secret the origins of investigations that have shaken the nation, deeply divided the electorate, and affected the future of the presidency.

From their point of view, it makes sense. Democrats were rattled by Republican efforts to uncover the origins of the Trump-Russia probe. The Steele dossier, the use of spies and informants to target the Trump campaign, the Carter Page wiretap, the murky start to the Crossfire Hurricane investigation -- Democrats resisted GOP attempts to reveal them all.

But in 2017 and 2018 Republicans controlled the House. Then-Chairman Devin Nunes used the power of the Intelligence Committee to unearth key parts of the story. Nunes' efforts eventually led to a Justice Department inspector general investigation whose results, expected in coming weeks, could further damage the Democratic Trump-Russia storyline. And then there is the ongoing criminal investigation led by U.S. Attorney John Durham.

But Democrats now control the House. As they lead the Trump-Ukraine impeachment inquiry, current Intelligence Committee Chairman Adam Schiff and other Democrats are applying the lesson learned from Trump-Russia: Do not allow inquiry into the origins of the investigation.

The problem is, the whistleblower remains an important part of the story. His carefully crafted Aug. 12 complaint created the template that Democrats have followed in the impeachment campaign. In public hearings, Democrats have praised the whistleblower's action for starting the whole process. And it's an incredibly important process -- what matter could be more weighty than possible removing the president of the United States? But the public does not get to learn how it began.

Behind the scenes, Schiff has exercised his authority to cut off lines of questioning that might reveal anything about the probe's origin. The transcripts of depositions his committee has released are filled with example after example of Schiff, or lawyers acting at his direction, stopping questioning that might lead to how the investigation began. "We want to make sure that there is no effort to try to, by process of elimination, identify the whistleblower," Schiff said in one recently released deposition.

Democrats learned several lessons from their unsuccessful attempt to bring down the president over the Trump-Russia affair. That investigation was entrusted to a special counsel who ultimately could not establish that Schiff's and the Democrats' key allegation, a conspiracy or coordination between Russia and the 2016 Trump campaign, ever actually occurred. Now -- lessons learned -- House Democrats are doing the Trump-Ukraine investigation themselves, making it easier to reach the conclusion they want.

But Democrats appear committed to not allowing Republicans to open the Pandora's box of how the investigation began. In the case of the Trump-Zelensky call, some officials heard the conversation as it happened and saw no wrongdoing. Others, or at least one other -- National Security Council official Lt. Col. Alexander Vindman -- saw wrongdoing and felt compelled to take action.

How did that happen, precisely? That is what Schiff does not want the nation to know.

Byron York is chief political correspondent for The Washington Examiner.