It may be politically expedient, per Pelosi, not to go right for impeachment, but I'm not sure the Democratic party can really claim to any integrity if it doesn't pretty soon. Part of the basis of representative democracy is that we elect people who are expected to know more than we do (or most of us, anyway) about how to secure the common good and protect democracy and the constitution.
Democrats were elected overwhelmingly in 2018 in large part due to a promise of oversight over an Executive Branch that is out of control. They have largely failed to do this, for various reasons, and I suspect will pay an electoral price in 2020 if they don't figure this out.
Pelosi says they are in a "fact finding" stage. I do think Democratic Leadership is playing down calls for an impeachment inquiry in an effort to not hamstring other lines of inquiry, while quietly laying the groundwork. Thinking was that if they went straight for the brass ring, the WH would cut off all access into emoluments, security clearances, inaugural donations, etc etc etc.
But, predictably, the Trump Admin is doing that anyway, with Trump's declaration that "We're fighting all of the subpoenas" a flat statement that he does not recognize Congress' Constitutional mandate to conduct oversight.
To be clear, this is a Constitutional crisis. One that ultimately will make real moves toward impeachment more likely. And then Trump thinks SCOTUS will protect him...lol.