U.S. President Donald Trump delivers a speech at the Economic Club of New York in New York, the United States, Nov. 12, 2019. Photo:Xinhua

US lawmakers on Monday careened toward the brink of one of the most divisive and momentous political steps in years: the impeachment of President Donald Trump for abuse of power and obstruction of Congress.

Days before the historic House vote, several congressional centrists, including some representing Trump-friendly districts, announced they will now support his impeachment, a boost for House Speaker Nancy Pelosi's effort to present a united front in her chamber's vote.

The group had been under intense political pressure from Trump and other Republicans eager to paint impeachment as extremist liberal overreach.

But seven freshman moderate Democrats published an opinion essay on Monday in The Washington Post explaining they were holding firm.

"We are veterans of the military and of the nation's defense and intelligence agencies," they wrote. 

"As members of Congress, we have prioritized delivering for our constituents.

"Yet everything we do harks back to our oaths to defend the country. These new allegations are a threat to all we have sworn to protect."

Among the authors was Elissa Slotkin from the swing state of Michigan, who faced a mixture of heckling and cheers when she discussed her decision at a town hall event.

"While we may not agree, I hope you believe me when I tell you that I made this decision out of principle," Slotkin said.

Slotkin acknowledged she could lose her job by voting yes, but "this is bigger than politics."

Polling shows Americans are almost evenly divided. A series of nationally televised hearings in recent weeks have failed to move public opinion, and signs of impeachment fatigue have emerged.

Even as Trump faces disgrace given the likelihood of his impeachment, a new poll shows his approval rating has inched upwards to a high point, although the figure remains underwater.

No Republicans publicly support impeachment, although congressman Justin Amash - who left the party this year and is now an independent - does. 

Lawmakers were beginning a consequential week. House Judiciary Committee Chairman Jerry Nadler released his panel's final report on Monday outlining the case for impeaching Trump and detailing his alleged wrongdoing, including pressuring Ukraine to investigate Democrats.