Reid enjoys broad support from Senate Democrats and is likely to retain his leadership post if Democrats hold the Senate.

But the issue of whether to express support for national Democrats is tricky for Democratic candidates running in conservative-leaning states.

Heitkamp has indicated general support for President Obama, but has criticized him publicly on multiple occasions — particularly on energy issues and leadership ability.

Emphasizing how toxic Republicans believe the association with prominent Democrats could be, Heitkamp’s likely opponent, Rep. Rick Berg (R-N.D.), called on her Thursday to denounce an attack ad “made by her Democrat ally and donor, Senator Harry ReidHarry Mason ReidDemocrats say change to filibuster just a matter of time The Hill's 12:30 Report - Presented by Connected Commerce Council - Biden faces reporters as his agenda teeters Biden hits one-year mark in dire straits MORE.”

The ad by Majority PAC, a super-PAC that Reid is supporting, criticizes Berg for voting to protect tax breaks for big oil companies, then accepting large amounts of money from the oil industry.

Berg’s campaign said the ad disparages the North Dakota energy that Heitkamp says she supports. Heitkamp’s team said Berg was attempting to distract from his voting record in the House and in the state legislature.