Former U.S. President Donald Trump’s unprecedented second impeachment trial kicked off on Tuesday as the Senate affirmed the constitutionality of the proceedings.

By a vote of 56 to 44, the Senate voted that it is constitutional to hold an impeachment trial for a former president. 

Six Republican senators joined all of the chamber’s 50 Democrats in deciding that Trump can face trial despite being out of office. 

The vote came after four hours of debate on the issue between Trump's defense team and the House impeachment managers. 

The vote on constitutionality required a simple majority, but the Democratic House managers will need to win over a total of 17 Republicans to convict Trump. 

The trial will continue on Wednesday noon, Eastern time, with House impeachment managers given eight hours to present their case, followed by Trump’s defense team. Both sides have two days to make their arguments before the Senate considers witnesses and then a final vote.