These midterm elections are in fact a kind of second presidential election
Traditionally, incumbent Presidents are in a weak position after two years in office. They usually lose one or two Houses. Maintaining the House of Representatives and the Senate’s status quo would be a great victory for Trump. If he loses the House of Representatives, but wins the Senate, then it will depend on the extent of the loss: either it is spectacular and he will be weakened, or he will still be in a good position and pursue his presidency.