A 6% swing from 2012 Iowa results (what IA HD28 was tonight) would give Dems a gain of 7 in the Iowa Senate (of the 25 seats that are up in 2018) and would swing the chamber back to Dems on a 27-23 margin. A 30% swing from 2016 Iowa results (what IA HD28 was tonight) would give Dems a gain of 11 seats of the 25 up in 2018 for a 31-19 majority in the state senate.
If we're to extrapolate these Missouri numbers, we get some interesting data from both. I'll first use MO HD50's -4.15 margin. I'm also just going to add up all the numbers here as Democrat and Non-Dem, so lumping in the Green+Lib+Other vote with Republicans to get a two party vote.
MO HD 50
2016 was Clinton, 37%, Non-Clinton, 63% (-26%)
2012 was Obama, 37.65%, Non-Obama, 62.35% (-24.7%)
2012 was McCaskill, 48.66%, Non-McCaskill, 51.34% (-2.68%)
A uniform swing statewide would've given Clinton a 21.85% swing, resulting in:
Clinton, 48.26%, Non-Clinton, 51.74
A uniform swing statewide would've given Obama a 20.55% swing, resulting in:
Obama, 54.68%, Non-Obama, 45.32%
And more important, a uniform swing statewide would've given McCaskill a -1.47% swing, resulting in:
McCaskill: 54.06%, Non-McCaskill: 45.94%
Now, if we're using MO SD28 with a D-19% margin...
2012 was McCaskill, 43.90%, Non-McCaskill, 56.16% (-12.26%)
And more important, a uniform swing statewide would've given McCaskill a -6.74% swing, resulting in:
McCaskill: 51.43%, Non-McCaskill: 48.57%