Republicans want to make sure they are “talking to their base” and not isolating any more voters, says Sky News Washington Correspondent Annelise Nielsen.

The impeachment trial of former president Donald Trump officially got underway in the US Senate on Tuesday (local time) with advocates for Trump arguing an impeachment of a former president is unconstitutional.

The first day ended with a vote on the whether the trial was constitutional with the Senate voting 56-44 to continue with the trial meaning six Republicans crossed the floor to vote with Democrats.

Ms Nielsen said this vote has “really given political cover” to those Republicans who aren’t entirely thrilled with the former president’s behaviour since the election loss in November.

“But at the same time, they still want to make sure they’re talking to their base and not isolating any more Republican voters.”