(CNN) On Thursday morning the House approved -- on a largely party-line vote -- a set of formalized rules to govern their ongoing impeachment inquiry into President Donald Trump's pressure campaign against Ukraine to force an investigation into Joe Biden.

The vote wasn't terribly surprising -- Democrats have a considerable majority in the House -- but that the party leadership decided to hold it at all was. After all, House leaders had resisted holding a floor vote to formalize the impeachment inquiry for weeks.

So, what changed their mind? Simple: Public opinion.

Remember that, at its root, impeachment is a political, not a legal process. And that past attempts to impeach presidents -- most notably Bill Clinton -- have had disastrous political consequences due to the majority party not paying enough attention to public sentiment.

That reality is why House Speaker Nancy Pelosi (California) was long reluctant to trigger any sort of impeachment inquiry, for fear that the public's lack of support for the impeachment and removal of Trump might boomerang back on her party with the 2020 election approaching.

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