Dogs and cats living together! Mass hysteria!
In reality, the biggest shift you need worry about is the appointment of another conservative to the Supreme Court. But even that isn’t certain. If history repeats itself, a Republican President will try to over-reach in his first two years, resulting in major losses in the House and Senate in 2018. That in turn will force the administration to work with Democrats in choosing a new Supreme Court justice, which would then be someone more like John Roberts than Clarence Thomas.
The checks and balances of government that the left has been trying so hard to get around will still be there, and the President will have limited power. Even if the Republicans hold the House and Senate, they won’t have huge majorities, and not every Republican in the Senate is a right-wing firebrand.
As for wars in the middle east - are you under the impression that those wars are already over? The Middle East is going to be a huge problem for the next President regardless of which party is in power, and you be almost assured that the result will be more American soldiers going there. You may not choose war, but sometimes war chooses you.
If Donald Trump is the nominee, I would not be surprised to see the Republicans lose the Senate, as there will be an awful lot of Republicans sitting home on election day. Expect Trump to try to run the country through the sheer force of his populist personality, with little regard for boundaries. He’ll surround himself with corporate crony types and do ‘deals’ as his method of governing. Yay.