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(CNN) —  

A Democratic senator facing a tough reelection fight in a deep red state on Sunday described the allegations against President Donald Trump as “serious” but said he is keeping an open mind when it comes to the Senate impeachment trial.

Appearing on ABC’s “This Week,” Sen. Doug Jones of Alabama said he has been reviewing information about the allegations that Trump used his office to pressure Ukraine President Volodymyr Zelensky to dig up dirt on a potential political rival.

“I’m trying to see if the dots get connected. If that is the case, then I think it’s a serious matter. I think it’s an impeachable matter,” he said. “But if these dots aren’t connected and there are other explanations that I think are consistent with innocence, I will go that way too.

“What I really want to see, though, is to fill in the gaps,” he said. “There are gaps.”

Jones stressed the importance of understanding the situation in its entirety.

“People can make up their mind with gaps in testimony, but I would like to see a full and complete picture. And we don’t have that because the President has refused to have his people come and testify and deliver documents,” he added.

Jones is among the more moderate members of his party in the Senate, although Alabama itself is still considered overwhelmingly Republican, and his seat is viewed as a top target for the GOP in 2020. A former prosecutor, Jones was elected to fill the Senate seat left open when Trump appointed Jeff Sessions to be attorney general, and his vote on impeachment is sure to be scrutinized in his reelection fight.

Last month, Sessions announced he will run to re-take his old seat, and repeatedly emphasized his strong support for Trump.

The House voted largely along party lines to impeach Trump last week. A Senate trial is expected to start next month, but House Democrats have held off on sending the two articles of impeachment, and appointing impeachment managers, to the Senate – saying they won’t do so until they see a “fair” structure for the trial.

The Senate’s impeachment trial of Trump is likely to end with his acquittal since conviction would require 20 Republicans to side with Democrats. There’s no sign that any Republican senators are ready to vote to remove Trump from office.

CNN’s Veronica Stracqualursi contributed to this report.