Historically, the party of the American president loses in the subsequent midterms. The reasons are usually obvious and predictable. Typically, the supporters of the party of the president become complacent and do not get out and vote for their local Congressional candidates with the same enthusiasm and commitment as they did for their president, two years previously.
The American people in general usually try to curb the power of the newly elected president indirectly; or try to punish the president and his party for presidential campaign promises not kept. In the midterms of 1994 and 2010, the GOP won majority control from the Democrats in the House of Reps during the first two years of the presidencies of Democratic Presidents Clinton and Obama.