At the top of the list are Tierney and Rep. David Cicilline (R.I.), two embattled incumbents in very Democratic states and in otherwise safe districts. Both face top-tier Republican recruits in November. …

Both parties face races and nominees that become unexpected headaches each cycle. But with a lack of an obvious political wave this year, Democrats have to hold and win many more seats than Republicans do, with little room for error. …

Rep. Francisco “Quico” Canseco (R-Texas) is one of the most vulnerable incumbents in the country, and Democrats are bullish on their recruit, state Rep. Pete Gallego. But there is a realistic chance he might not make it through the July 31 runoff with former Rep. Ciro Rodriguez, who has consistently raised fractions of Gallego’s quarterly fundraising hauls.