(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.

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