Connecticut Congressman Jim Himes, one of the top Democrats on the House Intelligence Committee, said he and his colleagues conclude their impeachment inquiry into President Trump by the end of year, setting the stage for a dramatic constitutional clash just months before the 2020 presidential election.

"My belief is that the speaker of the House would like to get this wrapped up by the end of the year. I think that's probably possible," Himes said on "Face the Nation" Sunday.

Himes said the probe, which his committee is spearheading, would move "much faster" if the White House would cooperate with congressional investigators. Denouncing the inquiry by the House as illegitimate, top White House lawyers have already said the administration will not willingly provide any testimony or documents to Democratic-led committees.

Despite the White House's efforts to discredit and obstruct the inquiry, Himes said House Speaker Nancy Pelosi is determined to finish the investigation before the year ends.

Himes also denied Republican accusations that the Democratic majority on the House Intelligence Committee is withholding documents from the minority. "That's not happening," he said, adding that sometimes he doesn't immediately get access to certain documents.

To defend the pace of the inquiry, the Connecticut lawmaker said the current probe is starkly different than those that were carried out during the presidencies of Richard Nixon and Bill Clinton, noting that lawmakers in both of those occasions had access to reports by special prosecutors about the alleged impeachable offenses.

"The Congress was handed a fully done investigation in the case of Clinton by special prosecutor [Kenneth] Starr. In the case of Nixon, by a different special prosecutor," Himes said. "We're doing that now and an investigation doesn't happen in the light of day."

Himes pledged that his committee will release the transcripts of the high-profile depositions it has recently overseen, saying they first need to be scrubbed for classified information.

In the last two weeks, the House Intelligence Committee, along with the Foreign Affairs and Oversight panels, have hosted several depositions from administration officials entangled in the campaign by Mr. Trump and his allies to enlist the help of the Ukrainian government in digging up dirt on political rivals, including the Biden family.

"The American people will see is that there is not one word of testimony, written or spoken, which contradicts the notion that the president used the assets of the United States — military aid, a White House meeting — to advance his political interests of getting Ukraine to meddle in the next, in the upcoming presidential election," he added.