Assuming nothing crazy happens, (though in the age of Trump, you never know) here's what I think.
Among the safe Ds and safe Rs, there are a few I'm gonna put a question mark next to. The first is Alabama's special election in November (I know it's not a 2018 election, but I'm putting it here anyway). Some primary polls suggest that Roy Moore might become the nominee, and for anyone familiar with Alabama politics, this guy brings disaster with him everywhere. If he gets the nomination, there isn't an 100% guarantee that he'd win a general. He could become the Republican version of Martha Coakley. Minnesota deserves a note because Trump nearly won it, but Klobuchar is quite popular. I know this sounds a bit like flawed thinking, but there's a very slight chance Cardin in Maryland isn't 100% safe. He hasn't announced he's gonna run for reelection, a popular Republican Governor (Hogan) is up for reelection, and Maryland hasn't been the kind of state that does a lot of ticket splitting. Hogan's coattails could overwhelm Cardin (or vice-versa) or another Democrat if Cardin retires.
Also, Bob Menendez has a corruption scandal going on, and is scheduled to appear in court in September, so he's not a 100% guarantee for reelection. I wish a competent Democrat would just primary him.
