I still think Trump's strategy is to keep his powder dry until after the midterms.
I do not trust any single poll. I believe the "most likely" scenario, is to hold or slightly lose the House, but to add seats in the Senate.
Trump NEEDS more Senate seats, to have a real majority for confirmations.
I further believe the dems strategy is to push as much as possible, although Impeachment+ removal is highly unlikely. But it weakens Trump.
I believe the dems remember they drove Nixon from office, without Impeachment.
And there is the matter of payback for Clinton who was weakened by Impeachment.
The only "grounds" necessary for Impeachment, are what the House says.