The case for impeaching Trump is based on the fact that Trump held up aid for Ukraine in order to coerce the country into opening politically advantageous investigations against a political opponent on his behalf. Trump has clearly not made the fight against corruption a priority in his administration. He's shown no interest in Ukraine except for debunked conspiracy theories he keeps repeating. This is an obvious abuse of power for personal benefit.

If we don't impeach Trump, that would effectively give permission to all future presidents to act as corruptly as they want—our system of checks and balances will fail. The president is not above the law. To support their case for impeachment, the House Judiciary Committee brought in four constitutional experts to clarify the case and rules for impeachment.

According to the New York Times, Harvard professor Noah Feldman argued Trump's actions rise to the level of impeachment for abuse of power:

“President Trump has committed impeachable high crimes and misdemeanors by corruptly abusing the office of the presidency,” Mr. Feldman said. “Specifically, President Trump abused his office by corruptly soliciting President Volodymyr Zelensky to announce investigations of his political rivals in order to gain personal advantage, including in the 2020 presidential election.”

Stanford law professor Pamela S. Karlan argued what Trump did is not politics as it's normally done—he was acting on his own behalf, not the country's.

“It is, instead, a cardinal reason why the Constitution contains an impeachment power,” she said. “Put simply, a candidate for president should resist foreign interference in our elections, not demand it. If we are to keep faith with the Constitution and our Republic, President Trump must be held to account.”