From the Megillah, we read that Mordechai put on sack-cloth and ashes upon hearing of Haman's decree. Esther, alarmed to see her cousin in such a state, sends him fine clothes to put on, but he refuses them (apparently, because he is "in mourning" due to the decree against the Jewish people).
Yet later, Mordechai was compliant with the King's order to dress him up in royal robes, wear a royal crown, and be paraded about by Haman. If he were in some state of mourning, he would refuse to get dressed up in fine clothing. At this point of the story, the evil decree is still in effect, and all of the Jewish people in the empire are in jeopardy.
So, two questions:
What exactly was Mordechai's rationale for not donning the clothing that Esther sent him, if not because he was in some sort of state of "mourning"?
Why would Mordechai refuse to put on the clothing for Esther, yet would be fine with Haman having him do so?
I'd appreciate answers that bolster their case with citations to Midrash, Talmud, etc. Todah!