The unprecedented second impeachment trial of former U.S. president, Donald Trump, begins in the U.S. Senate on Tuesday.

The trial marks the first time in history that a U.S. president is impeached after leaving office.

The U.S. has only had four presidential impeachments in its history, two of which was of Trump and took place over the last year.

No other president or federal official has been impeached twice.

The U.S. House of Representatives has charged Trump with incitement of an insurrection for his involvement in a deadly riot at the U.S. Capitol on Jan. 6.

In a brief filed on Monday, Trump’s lawyers asked the Senate to dismiss the case against their client.

Their defence is largely based on the argument that a president cannot be impeached after leaving office.

Many constitutional law scholars have dismissed this argument, however.

Trump was acquitted by the Republican-controlled Senate during his first impeachment, which took place in 2019 after he ordered a freeze on $391 million of security aid to Ukraine.

Congress had already approved the security aid.

The Senate must vote by a two-thirds majority to convict in impeachment, and Republican lawmakers were unwilling to vote against a popular member of their party.

It is likely that the same thing will happen in the second impeachment trial.

Democrats now control the Senate by the slimmest possible majority, but they do not appear to have the support of the necessary number of Republican lawmakers to convict Trump.

Like in the first impeachment, Trump has refused to appear before the Senate to testify. (dpa/NAN)