Apparently, the DCCC knows something the rest of us don't.
In 2012, two independent candidates, one of whom is listed as VoteforEddie.com (no longer available, if it ever was), challenged the Republican incumbent Mario Diaz-Balart, who then ran unopposed in 2014 and won by a substantial margin in 2016.
House Democrats Eye Districts Where Trump Won by Narrow Margin. (Morning Consult, 6/1/2017)
Rep. Mario Díaz-Balart won re-election in November by 25 points, while Trump’s margin was 1.7 points. Romney won the district by 9.6 points in 2012, half of McCain’s margin four years earlier.
Other Take Back the House 2018 posts:
Pennsylvania 8th. (6/2/2017)
New Jersey 11th. (6/2/2017)
Minnesota 2nd. (6/2/2017)
Nebraska 2nd. (6/3/2017)