Because Republicans were in charge, and because they hate and fear Trump as much as Democrats do, and for the same reasons.
I posted on Inauguration Day that Trump had six months to renounce the Republican party, to raise 435 candidates for the House elections of 2018, and to govern as a nationalist until both Republicans and Democrats in Congress could be replaced.
I was right.
I think the record indicates he did not have six months. He had no time. He was attacked long before he even took office.