The argument that House Democrats shouldn't impeach Trump because Senate Republicans won't convict is utter bullshit. House Democrats have passed all sorts of progressive legislation since taking control in January, only to die in the cold dead hands of Mitch McConnell. Should they not have bothered? What's the point of advancing legislation that has zero chance of being passed in the Senate and signed by the "president"? Would it be better instead for House Dems to sit on their hands and do nothing, because, you know, what's the use?
Of course not. Making arguments for and then DOING the right thing builds the case for why voters should turn control of the government back to the Democrats. If instead our elected leaders say "why bother?" - voters will respond in kind when Dems seek their support in 2020.
House Democrats must open an official impeachment investigation, and then after full, serious deliberation, vote on impeachment. All of this with the full knowledge that it will die in McConnell's Senate. That's not an argument not to impeach: it's proof that we cannot have a functioning democracy regulated by the rule of law with today's Trumpist Republicans in control. And it will be a rallying cry to win not only the White House but to flip the Senate as well.
All of the above is annoyingly obvious.
FFS.