The two dominant themes in the Democratic Party at this moment are: (1) "Just say NO" to impeachment, and (2) "Just say YES" to Joe Biden as the next Democratic candidate for President. Both of these themes are based on cynicism and a misreading of the lessons of recent political history.
Speaker of the House Nancy Pelosi has stood firm against impeachment because she believes it would put the Democratic majority at risk in 2020. She doesn't want to be seen as going after Trump for (perceived) purely partisan political reasons, which in her estimation will cause swing voters to abandon centrist Democrats in favor of right-wing Republicans, and cause the Democrats to lose their newly-won house majority. I believe she is wrong, both for practical reasons and, more importantly, for reasons of principle.
The practical: any defections among centrists would likely be negated by renewed enthusiasm from the left for the Democratic Party, who have waited for at least twenty years to see the party leadership grow a spine and actually fight for causes Democrats support. "When they go low, we go high" only works if your opponent hasn't already sliced your Achilles' tendons. (Why Hillary Clinton expressed "regret" for her "deplorables" remark remains a mystery to me.) The Democrats are constantly bringing knives to a gun fight. That's no way to win. But because of decades of misreading the electorate, the Democrats now are faced with the fact that if they are to gain any traction in government, they must overwhelm the Republicans with numbers on election day. The first step toward a wave election is to generate excitement on the part of voters. Weak-kneed politicians unwilling to fight for their base do not generate excitement.
The principle: the entire purpose of Article II, Section 4 of the US Constitution is to remove people like Trump from government.
The President, Vice President and all civil officers of the United States, shall be removed from office on impeachment for, and conviction of, treason, bribery, or other high crimes and misdemeanors.Robert Mueller concluded that Donald Trump did commit impeachable offenses; he just couldn't say so under the rules he was forced to work under - rules imposed by people who work for Donald Trump. Nancy Pelosi doesn't merely have the right to pursue impeachment, she has an obligation to do so, an obligation she accepted upon taking her oath of office and assuming the Speakership. Whether or not it hurts her party at the ballot box in 2020 she has a responsibility to the country to begin proceedings to remove Donald Trump from the office he has demeaned and abused for three years.
Next: why we shouldn't want Joe Biden as the Democratic presidential candidate.