May be - he simply sees all that impeachment thing to be utter sillyness (me - too). But - not sure, whether it's a sound reason to switch - he will NOT be welcome in Trump Republican party either.
Maybe he is centrist bipartisan independent maverick man who feels impeachment has gone too far (unlike GOP impeaching Clinton lying about getting a BJ which was totally based on principles and rule of law)
Dems should not punish Van Drew as voters only hold the left accountable for diverging too far from the ideological center and never hold the Republican party accountable for going too far right