Washington — House Democrats announced two articles of impeachment Tuesday against President Donald Trump, declaring he “betrayed the nation” in his actions toward Ukraine as they pushed toward historic proceedings that are certain to help define his presidency and shape the 2020 election.

The specific charges aimed at removing the 45th president of the U.S.: abuse of power and obstruction of Congress.

Speaker Nancy Pelosi, flanked by the chairmen of the impeachment inquiry committees, said somberly at the U.S. Capitol that they were upholding their solemn oath to defend the Constitution. Trump responded angrily on Twitter: “WITCH HUNT!” Voting is expected in a matter of days by the Judiciary Committee, and by Christmas in the full House. The charges, if approved, would then be sent to the Senate. The Republican majority in the Senate would be unlikely to convict Trump. But first there would be a trial filled with bitter accusations and recriminations just as voters in Iowa and other early presidential primary states begin making their choices.

In the formal articles announced Tuesday, the Democrats said Trump enlisted a foreign power in “corrupting” the U.S. election process and endangered national security by asking Ukraine to investigate his political rivals, including Democrat Joe Biden, while withholding U.S. military aid as leverage. That benefited Russia over the U.S. as America’s ally fought Russian aggression, the Democrats said.

Trump then obstructed Congress by ordering current and former officials to defy House subpoenas for testimony — some testified anyway — and by blocking access to documents, the charges say.

By his conduct, Trump “demonstrated he will remain a threat to national security and the Constitution if allowed to remain in office, ” the ninepage impeachment resolution says. After decrying the Democrats’ announcement, Trump headed to Pennsylvania for a reelection campaign rally.

First, he tweeted, “To Impeach a President who has proven through results, including producing perhaps the strongest economy in our country’s history, to have one of the most successful presidencies ever, and most importantly, who has done NOTHING wrong, is sheer Political Madness,.”

The outcome, though, appears increasingly set as the House presses ahead toward impeachment as it has only three times in history against U.S. presidents.

In outlining the charges, Democrats said they had no choice but to act because Trump has shown a pattern of behavior that, if left unchecked, poses risks to the democratic process ahead of the 2020 election.

“Our president holds the ultimate public trust. When he betrays that trust and puts himself before country, he endangers the Constitution; he endangers our democracy; he endangers our national security,” said Rep. Jerrold Nadler, D-N.Y., the Judiciary chairman, announcing the charges before a portrait of George Washington. “Our next election is at risk. … That is why we must act now.”

Nadler said, “No one, not even the president, is above the law.″