Why some Democrats are holding out on impeachment, in one chart

Why? The electoral map offers an explanation.

A new CNN analysis shows that House Democrats who support an impeachment inquiry represent districts with a 2016 margin of victory twice as wide as their Democratic counterparts who oppose an impeachment inquiry.

In short: The less competitive the district, the more likely a House Democrat is to support an impeachment probe.

In the 135 House districts represented by Democrats who support launching an impeachment inquiry, Hillary Clinton won by an average of 35 percentage points. But that average margin of victory shrinks to just half of that, 18 points, in the 100 House districts represented by Democrats who do not support launching an impeachment inquiry.

Further, in the 31 Trump districts represented by Democratic House members, only two of them -- Chris Pappas of New Hampshire and Lauren Underwood of Illinois -- support an impeachment inquiry.

Overall, the data marks a shift toward the mainstream for impeachment proponents since last January, when a CNN analysis found Clinton's margin of victory was a much larger 46 points in pro-impeachment districts vs. 28 points in anti-impeachment districts, based on a January 2018 vote on the floor.

In fact, a broad 30 of the 38 Democrats representing the most anti-Trump districts support an impeachment probe. But only 5 of the 38 Democrats representing the strongest Trump districts support an impeachment inquiry.

The Democrat in the most anti-Trump district who still doesn't support an impeachment inquiry? Speaker of the House Nancy Pelosi.

"We have been having an investigation -- in case you missed it -- for a very long time," Pelosi said earlier this week. "I do know that we've been on the path to (investigate) and that includes the possibility of legislation or impeachment."

The House Judiciary Committee approved a resolution on Thursday to outline potential impeachment proceedings against Trump. The committee's chairman, Democratic Rep. Jerry Nadler of New York, says the move will strengthen the committee's ability to conduct its investigation.

But Democrats are divided on whether a formal impeachment inquiry is already underway. Nadler said on Monday that his panel is indeed performing an impeachment inquiry, though other top Democrats have framed it as merely a continuation of ongoing probes.

Nadler appeared tired of the debate surrounding what to call his investigation Thursday.

"Some call this process an impeachment inquiry," Nadler said. "Some call it an impeachment investigation. There is no legal difference between these terms, and I no longer care to argue about the nomenclature."

Impeachment would require a majority vote in the House of Representatives, but removing the President from office would require an unlikely two-thirds vote in the Republican-led Senate.