Here is Crystal Ball’s current Senate ratings
Currently, Sabato believes Johnson (R-WI) and Kirk (R-IL) will flip from R to D. Crystal Ball projects that Trump would also cost Toomey (R-PA) and Ayottee (R-NH) their seats. Portman’s lean R race in OH becomes a toss up, while the races to replace Reid in NV and Rubio in FL go from toss up to Lean D. There are no R pick ups under either scenario. Overall, a Senate majority should be achievable for the Democrats in 2016 given that Trump will be the nominee.
However, even with the scenario of Trump “hurting” Republicans down the ballot, Crystal Ball projects that Rs would have the Senate filibuster and the House if America chooses to have its first female president.
Even if HRC wins, she’s still weaker than Obama before the 2010 midterms. Gridlock would be the norm (McConnell’s priority would again be to ensure HRC is a one term president by obstructing). Trump gets to spend 2016–2020 nitpicking at Clinton’s every mistake, blaming her for gridlock that both sides cause, and then thumping his chest on TV for free when the business cycle goes through an inevitable correction. Trump 2020 is a winner in that scenario.
Of course, Trump could get the White House (let’s say if the FBI puts laws before country and sends Clinton to big house), but it’s extremely unlikely given his low approval ratings among woman and Hispanics.