WASHINGTON (Reuters) - The U.S. Senate on Tuesday will hear opening arguments in an impeachment trial to determine whether to remove President Donald Trump from office on charges that he abused his power and obstructed Congress in its investigation of his dealings with Ukraine.

The following explains the two charges, or “articles of impeachment,” approved by the U.S. House of Representatives.

ABUSE OF POWER

In the impeachment context, abuse of power is generally defined as using the vast powers of the presidency for personal benefit.

The abuse of power cited in the House articles of impeachment included Trump’s withholding of $391 million in security aid for Ukraine, which Democrats have said was aimed at pressuring Kiev into investigating political rival Joe Biden, the president’s possible Democratic opponent in the Nov. 3 election.

Abuse of power is not specifically referred to as an impeachable offense in the U.S. Constitution, which states that a president can be removed from office for “Treason, Bribery, or other high Crimes and Misdemeanors.” But many legal scholars have argued that the founders of the United States intended the phrase “other high Crimes and Misdemeanors” to broadly encompass abuses of power.

Alexander Hamilton, a famed American statesman, wrote in 1788 that impeachment proceedings were for “those offenses which proceed from the misconduct of public men, or, in other words, from the abuse or violation of some public trust.”

Abuse of power was one of the articles of impeachment advanced against President Richard Nixon, who resigned before a full House vote on the charges. In approving the charge of abuse of power against Nixon, a House committee accused him of authorizing tax audits of political opponents on his “enemies list.”

Abuse of power was advanced as an article of impeachment against President Bill Clinton relating to his affair with a White House intern, but a majority of House members voted against including that charge. Clinton was eventually impeached on two other charges - perjury and obstruction of justice - but was not convicted by the Senate.

OBSTRUCTION OF CONGRESS

Democrats have also charged Trump with obstruction of Congress based on his stonewalling of the House’s impeachment inquiry. The White House has refused to provide documents to congressional investigators and has instructed top advisers and government officials to defy subpoenas and refuse to testify.

A similar charge, contempt of Congress, was one of the articles of impeachment against Nixon, who had defied subpoenas for incriminating tape recordings.

Contempt of Congress is a misdemeanor crime under U.S. law, which defines the offense as willfully failing to provide testimony or documents to Congress. A different crime, obstruction of justice, more broadly prohibits “interference with the orderly administration of law and justice.”

The White House has argued that the Constitution does not require senior presidential advisers to appear for compelled testimony before Congress. A judge rejected that argument on Nov. 25 in a dispute over a subpoena issued to former White House counsel Don McGahn. The White House has appealed that decision.

Trump’s lawyers have also argued his refusal to cooperate with the impeachment investigation is justified because the process has been unfair to him.