"I've got this set of doubts," the purple-state senator says.
The DSCC wants to know if Republicans will meet with the presumptive GOP nominee.
Sen. Mark Kirk said he is the "best-positioned Republican" to avoid being linked to Trump.
The Senate minority leader showed he will be a vocal critic of the presumptive Republican nominee.
Ted Strickland is hitting Sen. Rob Portman over a report that he could be Trump's running mate.
Sen. Richard Burr says he will support Trump as the nominee.
Democrats are tying vulnerable Senate incumbents to Trump after his win in Indiana.
The new web ad follows a $2 million TV and digital ad buy in Wisconsin earlier this week.
Ayotte faces a tough reelection fight to keep her Senate seat.
Young will face off with former Rep. Baron Hill in November for the open Senate seat.