Montana Sen. Jon Tester (D) led by 4 points in his bid for re-election with two-thirds of precincts fully reporting early Wednesday morning, but enough votes remained outstanding that the race was too close to call.

Tester led with 49 percent, while his Republican challenger, Rep. Denny Rehberg, had 45 percent. Libertarian candidate Dan Cox appeared to be giving Tester a significant boost by taking more than 6 percent of the vote.

“The good news is: The hard part is done,” Tester told supporters at 4 a.m. ET, according to his spokesman. “All that door-knocking, all those phone calls, all that worn-out shoe leather — it all comes down to this. But we’re not celebrating a victory quite yet.”

The only other outstanding Senate race is in North Dakota, where former state Attorney General Heidi Heitkamp (D) held a small lead over Rep. Rick Berg (R).

Democrats will retain control of the Senate no matter the outcome of either race. Victories in either would mean they actually expanded their majority.