That would mean beating every Democrat running...plus a few more who are not running.
Somehow I don’t see us winning every Democrat seat and keeping every Republican seat, no matter how unpopular the Democrat “brand” may be in November. 25 of the 36 races include incumbents, and those races are going to have a lot more to do with the popularity of the incumbent than with national partisan politics.
For instance, here in North Carolina, I don’t like Richard Burr’s chances at re-election no matter how effective a national campaign the Republicans run. He isn’t particularly popular, and having an (R) behind your name isn’t enough by itself (even in years when the national mood favors Republicans),to win over the Jessecrats who hold the balance of power here.
National politics will weigh more heavily in the 11 open seat elections, and I think Republicans will do well there, but we can’t make any general, national assumptions about the incumbent races - they’re too heavily dependent on state politics.