Outside donor groups could tip one of the most closely watched elections of the midterm cycle.
The Koch groups are worried that tariffs and a trade war with China would offset any potential positive economic gains from the GOP's tax cuts.
Brian Walsh, the head of the nonprofit Trump advocacy group America First Policies, told CNBC that there's a lack of polling data to suggest a trade war will hurt Republican efforts this year.
Tim Pawlenty, who had already served two terms as Minnesota's governor, will be trying to flip a seat that's been held by Democratic incumbent Mark Dayton for the past seven years.
White House lawyers and Bolton continue to discuss and review any potential conflicts of interests for the former U.N. ambassador, sources with direct knowledge of the matter told CNBC on the condition of anonymity.