US President Donald Trump has objected to the House of Representatives' articles of impeachment, accusing Democrats of "perversion of justice and abuse of power" in their effort to remove him from office.

Key points: Mr Trump maintained he did nothing wrong in seeking foreign investigation of political rivals

Mr Trump maintained he did nothing wrong in seeking foreign investigation of political rivals The House Of Representatives will debate two articles of impeachment against Mr Trump

The House Of Representatives will debate two articles of impeachment against Mr Trump House Speaker Nancy Pelosi has warned against pursuing a strictly partisan impeachment

In a fiery letter sent to House Speaker Nancy Pelosi on the eve of his expected impeachment, Mr Trump maintained he did nothing wrong in seeking foreign investigation of political rivals, and attacked the Democrats for focusing on impeachment rather than other issues.

He also repeated his objections to the process of the House inquiry, claiming "more due process was afforded to those accused in the Salem Witch Trials".

Mr Trump said he did not believe his letter would change anything, but he was registering his objections "for the purpose of history".

House Democrats and Republicans sparred over the rules of debate for the historic votes on impeaching Mr Trump, dispatching the lofty rhetoric of constitutional duty for the rugged politics of the House action and Senate trial that is expected to follow.

The Democratic-majority House Rules Committee met on Wednesday, with politicians arguing over the parameters for the debate, which is expected to culminate in votes to make Mr Trump the third president to be impeached in United States history.

Nancy Pelosi has warned against pursuing a strictly partisan impeachment. ( AP: J. Scott Applewhite) )

"It's unfortunate that we have to be here today, but the actions of the President of the United States make that necessary," chairman Jim McGovern said. "The evidence is as clear as it is overwhelming."

He said Mr Trump "jeopardised our national security and he undermined our democracy," adding that "every day we let President Trump act like the law doesn't apply to him, we move a little closer" to rule by dictators.

Republicans firmly disagreed.

No Republicans are expected to vote to impeach Mr Trump

Republican Tom Cole said half of Americans were telling the House that "what you are doing is wrong". ( AP: The Flint Journal, Jake May )

The top committee Republican, Tom Cole of Oklahoma, said the split view among Americans over impeachment should be reason enough not to proceed with the rare action.

"When half of Americans are telling you what you are doing is wrong, you should listen," he said.

House Democrats are planning to launch the debate on Thursday and, likely vote to impeach Mr Trump by formally accusing him of abusing his power as President in dealing with Ukraine to help himself politically and then obstructing Congress by blocking the later investigation.

No Republicans are expected to vote to impeach Mr Trump. But one-by-one Democrats are amassing a majority from their ranks, including many freshmen who could risk their re-election chances from districts where Mr Trump is popular.

Speaker Nancy Pelosi, who warned against pursuing a strictly partisan impeachment, is now all but certain to have the numbers.

As impeachment appears set in the House, attention is shifting to the Senate which, under the constitution, is required to hold a trial on the charges. It is expected to begin in January.

Hoping to dispatch with lengthy proceedings, Senate Majority Leader Mitch McConnell rejected the Democrats' push for fresh impeachment testimony in a last-ditch plea for the House to "turn back from the cliff" from the expected vote.

Mr McConnell's remarks effectively shut the door on negotiations for a deal proposed by the Democratic leader, Senator Chuck Schumer, who wants to call top White House officials for the Senate trial, which is set to start next year if the House impeaches Mr Trump this week.

"If House Democrats' case is this deficient, this thin, the answer is not for the judge and jury to cure it here in the Senate," Mr McConnell said.

"The answer is that the House should not impeach on this basis in the first place."

Mr Schumer's proposal was the first overture in what were expected to be negotiations between the two leaders over the contours of a weeks-long trial.

Mr Trump wants a more showy proceeding to not only acquit but vindicate him of the impeachment charges from the House, though he has instructed officials not to appear in the House.

Mr McConnell and most GOP senators prefer a swift trial to move on from impeachment.

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AP