Senator Doug Jones of Alabama says he could vote to acquit President Trump in his upcoming impeachment trial if his Democratic colleagues don’t ‘connect the dots’ and prove his guilt.

The Democrat, who faces a tough re-election fight - possibly against his predecessor, former US Attorney General Jeff Sessions - said the allegations against the president were ‘serious’ but he is open to voting not guilty because of ‘gaps’.

‘I'm trying to see if the dots get connected,’ Jones told ABC News on Sunday.

‘If that is the case, then I think it's a serious matter. I think it's an impeachable matter.

Senator Doug Jones, the Democrat from Alabama, says there are 'gaps' in the case against President Trump (right) and that he could vote to acquit if his party fails to 'connect the dots'

‘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.’

The Democratic-led House of Representatives approved two impeachment charges against Trump on Wednesday over his pressuring of Ukraine to investigate a political rival, Joe Biden.

There is little chance he will be convicted and removed from office through a trial in a Senate controlled by fellow Republicans.

Democrats are pushing to call top Trump aides to testify, but Senate Majority Leader Mitch McConnell wants the Senate to consider the case without hearing from new witnesses.

Jones told ABC News on Sunday that he is in no rush to make up his mind.

‘People can make up their mind with gaps in testimony, but I would like to see a full and complete picture,’ the senator from Alabama said.

‘And we don't have that because the president has refused to have his people come and testify and deliver documents.’

Jones is in a difficult predicament. A moderate Democrat, he represents a state that is overwhelmingly pro-Republican.

Jeff Sessions, Trump's former attorney general, entered the race for the Republican nomination for the US Senate seat from Alabama. Sessions was senator from Alabama for 20 years before he was appointed by Trump to head the Justice Department in 2017

A former prosecutor, Jones narrowly defeated Republican former judge Roy Moore in the 2017 special election held to fill Sessions’ seat when he was named by Trump to head the Justice Department.

During the campaign, several women came forward and accused Moore of sexual misconduct. Three women alleged Moore assaulted them when he was in his 30s.

Two of those women say they were minors when the alleged incidents took place.

A poll of likely voters in Alabama shows Jones trailing hypothetical Republican opponents - with the exception of Moore.

Tommy Tuberville, the former head coach of the Auburn University football team, has a seven-point lead over Jones, according to the Mother Jones news site.

If Sessions, who held the Alabama senate seat for 20 years, were to face Jones, he would also be projected to beat him. Sessions gets 46 per cent of the vote, while Jones gets 41 per cent.

Polls show Jones trailing other potential GOP candidates, including former college football coach Tommy Tuberville (left) and US House Rep. Bradley Byrne (right)

Another potential Republican candidate, House Rep. Bradley Byrne, leads Jones by four points.

If Moore were to somehow win the Republican primary and face Jones, the Democrat would have a significant advantage - 47 per cent to 33 per cent.

Voters in Alabama will keep a close watch on how Jones votes. If he votes to convict Trump, it will likely anger the state’s more conservative voters.

But if he breaks with his party and votes to acquit, Jones could spark a backlash from his core base of liberal supporters.

Jones was asked if he agrees with House Speaker Nancy Pelosi’s move to hold on to the articles of impeachment and not send them to the Senate until Democrats receive assurances that they can call witnesses.

‘I certainly don't think it's unfair for her to do that,’ Jones said, citing the Bill Clinton precedent.

‘You know that the Clinton articles of impeachment were voted on around December 17th,’ Jones said.

‘They didn't come over to the United States Senate until around January the 6th or 7th. Some three weeks later.’

He continued: ‘I think what the speaker is doing is saying, “What are the rules going to be when I send house managers over there? What kind of playing field are we going to have? What is the timing?”

Jones narrowly defeated Republican former judge Roy Moore (above) in the 2017 special election. During the campaign, several women came forward and accused Moore of sexual misconduct

‘I don't think that's unreasonable to try to just simply ask that the Senate majority leader and minority leader to sit down, establish those rules going forward before she sends the articles over.’

‘She's not going to hold these forever.’

When asked if he was worried that a vote against Trump would doom his chances of re-election in Alabama, Jones said: ‘I took an oath as a US senator.

‘I'll take another oath, and that's where my duty is.

‘The problem we have in America today, and the problem we have sometimes with all due respect in the media, everybody wants to talk about this in the political terms and the political consequences term.

‘This is a much more serious matter than that.

‘This has to do with the future of the presidency, and how we want our presidents to conduct themselves, and it has all to do with the future of the senate, and how a Senate should handle impeachment, articles of impeachment that come over.’