To my understanding, it wouldn't be wise, because implementation of martial law would be immediatly branded as "a military coup d'etat" and DT " a dictator"

We just experienced how mighty media machine is and what kind of power big Tech has.
Note, that so far, DT and his team pursued only legal path, applying all accessible and constitutional measures to resolve a problem.
And the further it went, the more murky area appeared...all institutions, from courts of law to Congress have failed. Nobody even tried to listen to the voice of people. If there are well documented cases of massive vote fraud, it would be the best way to win through a legal battle.