An American University professor who has correctly predicted the last nine presidential elections says President Trump will win the 2020 election unless congressional Democrats, "grow a spine," CNN reported.

Allan Lichtman, a political historian, said Democrats only have a shot at the White House if they begin impeachment proceedings against Trump, calling the decision both "constitutionally" and "politically" right in the wake of special counsel Robert Mueller's investigation into Russian interference in the 2016 presidential election.

"It's a false dichotomy to say Democrats have a choice between doing what is right and what is constitutional and what is politically right. Impeachment is also politically right," Lichtman told CNN's Brooke Baldwin on Wednesday.

Lichtman has developed a system of 13 "key factors" that help determine whether the party in the White House will maintain its hold, according to CNN. The factors range from whether the party has an incumbent president running to the country's short- and long-term economic conditions to foreign policy successes and failures. If the party loses out on six factors or more, he says they will lose the presidency.

Lichtman says the Trump administration is down three key factors: Republican losses in the midterms elections, a "lack of foreign policy success" and Trump's "limited appeal to voters," CNN reported. Impeachment would trigger a fourth key - scandal over the proceeding's public nature.

"Let's not forget, impeachment is not just a vote in the House," Lichtman said. "It involves public hearings as part of the impeachment inquiry, and, what everyone forgets, a public trial in the Senate in which House prosecutors present evidence, present documents, make opening and closing statements."

Lichtman cited scandal as a central factor in former Vice President Al Gore's loss in the 2000 presidential election after President Clinton's impeachment process.

"Democrats are fundamentally wrong about the politics of impeachment and their prospects for victory in 2020," Lichtman told CNN's Chris Cillizza on Tuesday.