The United States Senate is on Friday expected to vote on whether to call witnesses in President Donald Trump’s impeachment trial.

This after both the prosecution and defence fielded questions from senate jurors over the last two days.

Democrats have backed calls by their impeachment managers that former National Security Advisor John Bolton be called to testify after a leaked draft of his upcoming book revealed that President Trump directly tied the release of military aid to Ukraine to them launching an investigation into a political opponent.

However, Republicans are close to united in blocking any motion to call witnesses.

If the Republican leader succeeds in blocking the motion to call witnesses, the Senate could move swiftly to vote on the two articles of impeachment, namely the abuse of power and the obstruction of Congress.

A number of moderate Republicans earlier indicated they would be open to calling witnesses, but backroom dealings by Grand Old Party (GOP) leadership and the White House appears to have brought them into line although nothing has been confirmed as to what the final tally would be.

Democrats, who are the minority party in the Senate, require the backing of four Republicans and no defections for a simple majority vote to force witnesses to be called.

Many Republican Senators have indicated they’ve heard enough evidence and are keen to move towards a final vote on the charges that will in all likelihood acquit the President.