There were ten separate incidents Mueller laid out where he presented evidence that Trump obstructed justice or attempted to obstruct justice. He left it to Congress to take action. Throw in the two campaign finance felonies from SDNY where he is named as an unindicted co-conspirator and I have to ask if you don't Impeach Trump who do you Impeach?
Not impeaching Trump for these crimes nullifies Impeachment as a remedy as it is spelled out in the constitution forevermore. The duty that comes along with the oath of office requires Impeachment no matter how politically speaking bitter you think that pill is to swallow.
Historically, Democrats have never been rewarded at the ballot box for timidity. For example, how did it turn out for Democrats when they passed the Republican healthcare plan? (Romney care) They should have been bold then and passed a real comprehensive healthcare plan and not simply insurance reform. Republicans called their own plan socialism and communism so it's not like they could have said anything worse about an actual single-payer plan.
What do Democrats thinks makes this different? They should be making their case to the American people that Trump committed numerous crimes and he is not above the law. Here is a prediction for my fellow Democrats. If they roll over on this, and it looks like they will, Trump will win reelection because Republicans will pound this issue over and over about how Trump was subject to a witch hunt, the report exonerated him and so on. A second term of the criminally corrupt Trump who has now managed to surround himself with toadies that will willingly break the law will do permeant damage to our system of government.
