While I'm fairly sure that part of the deal he made with the GOP to keep running was that they would not fund a primary candidate against him...I'm even more certain he will not be reelected to the US Senate.
If there is not a grassroots challenger in the primary (look for a very rich man), there will be a "moderate" democrat that cleans his clock in the general.
"Ted Cruz was a Canadian Citizen when he asked for our vote 6 years ago. He deceived us by not disclosing that fact, one which he most certainly was aware".
Yes, the 2018 Senate race will be interesting on many levels. I fully expect President Trump will be taking careful notes of who has supported and who has opposed his administration in its first two years and will be prominent on the campaign trail to help clear out the congressional “dead wood”.