There are two factors, in a way at odds with each other, that are nonetheless entrenching their respective positions. On the one hand, it’s Pelosi who has more to lose with any politically tough vote because her party holds the majority, and Republicans want her incumbents who represent districts Trump won to go on the record now and as often as possible.
“It’s not popular” in Democratic-held districts that Trump won, said Michael Steel, who served as an aide to former House Speaker John Boehner, R-Ohio. “They think the Democrats in swing districts will suffer blowback.”
And Trump would like to see a party-line vote, which could bolster his argument that Democrats are dividing the country unnecessarily for political gain.
On the other hand, public opinion is shifting away from the president , meaning it’s getting easier for rank-and-file Democrats to vote in favor of impeachment and perhaps a bit harder for a handful of Republicans to vote against it. The sooner Trump gets a vote, the less likely he is to see Republican defections. And, if he can force Pelosi to hold an impeachment inquiry vote, it would be extremely difficult for any Republican who votes against that to cast a vote for impeachment later.