How would that seem to be unlawful? Stinky does not equal illegal.Evidence of a crime....conspiring with Giuliani to pressure a foreign government to investigate a political rival. That seems sufficient grounds for a congressional inquiry.
Is it unlawful? On the surface, it would seem to be. If the president had acted in the interests of the United States, I think he would be within the law and within the scope of his executive authority. Using Giuliani rather than normal channels raises the stinkiness of the president's actions and motives.
An inquiry is appropriate. Whether that results in a formal impeachment remains to be seen.
It is amazing how far some people are willing to go to get Trump. This impeachment attempt is even worse than the Clinton impeachment.
Basically it all comes down to, "we don't like him, so we must impeach him!"