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DENVER (KDVR) — Colorado’s Senate race heated up Friday night, with the third debate between incumbent Sen. Cory Gardner and his challenger, former Gov. John Hickenlooper.

The two had a 90-minute debate that was streamed on Colorado Public Radio. They’ve debated twice in the last week and have one more debate scheduled for Tuesday.

These debates come at a critical time. Colorado ballots started being mailed out Friday.

The latest poll for the Senate race shows Gardner has made up a bit of ground, according to Survey USA, which conducted the poll for Colorado Politics.

The poll shows Hickenlooper with a nine point lead. With less than a month before the election, 8% of Colorado voters are still undecided about the Senate race. Plus, the poll has a margin of error of 3.9%, which shows that Gardner is not out of the race entirely.

Colorado’s Senate race is one of the most important in the country. Democrats need to net four seats to take control of the Senate, or net three seats and win the White House. Gardner is one of the most vulnerable Republican Senators who’s up for re-election and Democrats are counting on Hickenlooper winning the race.