Polls released Tuesday show Montana Gov. Steve Bullock (D) leading incumbent Sen. Steve Daines (R) by 7 points (sample size: 738) and North Carolina Democratic candidate Cal Cunningham beating Republican Sen. Thom Tillis by 9 points (sample size: 1,362).

Other recent numbers show an upward trend for Democrats:

Arizona: Democratic frontrunner Mark Kelly leads Republican Sen. Martha McSally by 8 points in the Real Clear Politics polling average.

Kansas: Democratic frontrunner Barbara Bollier led possible Republican nominee Kris Kobach by 2 points in a recent Public Policy Polling survey.

Maine: Sara Gideon (D) has a 2.5-point lead over Republican Sen. Susan Collins in the Real Clear Politics average.

Iowa: Sen. Joni Ernst (R) leads possible challenger Theresa Greenfield (D) by a point in a new Public Policy Polling survey.