I truly believe Trump has been blessed by God.
He is extremely fortunate in the fact that Democrats have far more Senate seats up for re-election vs. the number up for re-election for Republicans.
Currently, Democrats have 24 seats up for election, including the seats of two independents who caucus with them. Republicans have nine seats up for election. The seats up for regular election in 2018 were last up for election in 2012; in addition, special elections will be scheduled if vacancies occur, as has already happened in Minnesota and Mississippi.
It's virtually impossible for Republicans to lose the Senate, even in a Democrat wave election. The only vulnerable Republican seats are AZ and NV, while Democrats have to defend about 10 seats in states that voted for Trump.
The good news, is that with a Republican Senate, Trump can keep getting Judges and other nominees confirmed despite united Democrat opposition.
The House, unfortunately, is another matter but I think Republicans will hold it. Not that Paul Ryan has done any good for Trump, but a Democrat majority could create a lot of extra mischief.