It’s very weird that, since Michael Cohen’s testimony, many pundits, a fair number of whom, were opposed to impeachment, are now calling for impeachment. As we’ve noted previously, the violations of the emoluments clause (in the U.S. Constituion) are enough for impeachment. That said, if Trump does get impeached (charges are brought–I doubt the Senate would act), I think the focus won’t be on the Mueller probe or Michael Cohen, but on the emoluments issue–because it is so obvious and so easy to document.
Put another way, the U.S. Congress, had it been so inclined, already had legitimate grounds to impeach. It choose not to do so.