The AP has projected that Montana Democrat Jon Tester will win re-election against Republican Rep. Denny Rehberg.
That leaves just the North Dakota senate race undecided. Fewer than 3,000 votes separate Democrat Heidi Heitkamp and Republican Rick Berg, according to the most recent vote information.
Tester's victory, after a tough election fight that saw Montana flooded by advertising from outside groups like Karl Rove's American Crossroads, means Democrats will hold every one of the seats they flipped in 2006 to get them the senate majority.
Tester was first elected in among the class of Democrats who took Republican seats that year: Claire McCaskill from Missouri, Bob Casey from Pennsylvania, Sherrod Brown from Ohio, Sheldon Whitehouse from Rhode Island, Jim Webb from Virginia.
Democrats held on Tuesday night to every one of those seats they flipped back in 2006. Only Webb left the senate. He was replaced by Democrat Tim Kaine, who defeated former Sen. George Allen, the Republican unseated by Webb.