After two weeks of public hearings, the House impeachment inquiry into President Trump is approaching its next stage: lawmakers are now writing a report that could lead to articles of impeachment.

House Intelligence Committee Chairman Adam Schiff, D-Calif., made the rounds on Sunday television programs outlining the case for impeachment without outright saying whether Trump will be the third president in United States history to be impeached.

"The evidence is already overwhelming," Schiff said on CNN's State of the Union. "The facts are really not contested. It's really not contested what the president did."

At the center of the inquiry is a July 25 phone call in which President Trump asked Ukrainian President Volodymyr Zelenskiy to investigate former Vice President Joe Biden and his son, Hunter. The president also suggested that Ukraine look into a debunked conspiracy theory that Ukraine, not Russia, was responsible for 2016 election meddling. The U.S. intelligence community has traced that attack to Russia.

Impeachment inquiry witnesses have testified that $391 million in security assistance to Ukraine was frozen in order to pressure the country to mount the requested investigation. President Trump has denied the allegation, saying there was "no quid pro quo" in his dealings with Ukraine.

There are no more public hearings scheduled in the alleged pressure campaign on Ukraine, but Schiff said investigators are still willing to summon additional witnesses.

"We don't foreclose the possibility of more depositions, more hearings," Schiff said on CNN. "We are in the process of getting more documents all the time. So that investigative work is being done."

Some key witnesses in the inquiry have defied subpoenas, citing legal murkiness over whether Congress can enforce subpoenas when the White House is ordering the targets of the those requests not to cooperate.

A ruling on that question is expected on Monday.

U.S. District Judge Ketanji Brown Jackson, who is presiding over a case involving former White House counsel Donald McGahn, wrote in a court filing that she intends to rule before the close of business Monday, "absent unforeseen circumstances," according to an order filed in the case.

During a hearing last month, Jackson peppered Trump lawyers with questions as the administration's legal team argued that the White House's theory of "absolute immunity" should shield former top administrative officials from having to comply with requests to appear for questioning.

"So what does the separation of powers mean to you then?" Jackson asked Trump administration lawyers in late October. "How can the legislature actively exert its oversight power unless it has the ability to exercise its investigative powers?"

Jackson's ruling is being closely watched as other potential witnesses consider whether to cooperate with Congress.

Among the witnesses who House investigators are pursing but who have refused to cooperate are White House acting chief of staff Mick Mulvaney, Vice President Mike Pence, Secretary of State Mike Pompeo and Trump's personal lawyer, Rudy Giuliani.

Instead of fighting to have these witnesses appear before House lawmakers, Schiff has decided to press forward with the impeachment report, indicating that drawn-out court battles would prolong a process that needs to move swiftly.

"What we're not prepared to do is wait months and months while the administration plays a game of 'rope a dope' in an effort to try to stall," said Schiff, referring to the boxing technique of feigning to be trapped against a ring's ropes to force an opponent to throw punches that will untimely prove fatiguing.

Schiff said the committee is learning more every day but that the evidence already collected is so "overwhelming and uncontested" that Democratic lawmakers decided to begin writing a report on the findings for transmission to the House Judiciary Committee, which would draft any articles of impeachment.

While polling suggests Americans are divided on whether Trump should be impeached, some polls have shown impeachment support weakening in critical battleground states, like Wisconsin. Speaking on CNN, Schiff said he does need to consult with other lawmakers and his constituents before making a decision on impeachment. At the same time, Schiff said next year's election should not influence the final determination.

"And if we decide our duty is to impeach, then we need to make the case to the American people, and we have to hope that we are successful in making that case," he said. "But this shouldn't be driven by what we think helps us in 2020 or hurts us in 2020."

Republicans in Congress on Sunday came to the president's defense, dismissing the impeachment probe as a political hit job and saying there is insufficient evidence to impeach.

"I think it has been very confusing to the American public as they followed this because there's no impeachable offenses," Rep. Elise Stefanik, a New York Republican on the House Intelligence Committee, said on Fox News' Sunday Morning Futures. "I think every single day that the American people are able to tune in, they see that this is a partisan process."

A vote on articles of impeachment could happen before Christmas, setting up a Senate trial some time in 2020.

On Friday, Trump shifted his tone by saying he is welcome to a trial in the Republican-controlled Senate.

"Frankly, I want a trial," Trump said.