What started as a pipe dream for liberals who hoped Congress would impeach President Donald Trump is now progressing steadily to reality, with a growing sense on Capitol Hill that the historic and rare formal charge against the president is inevitable.

Several national polls taken after allegations surfaced the Trump sought foreign government help in his re-election effort show a jump in support for impeachment among voters. More than 300 former national security officials – some of whom worked for presidents in both major parties – signed a letter Friday saying the president's actions raise a "profound national security concern," and that they supported an impeachment inquiry.

Congressional Democrats who have long supported such a move say they see a change in their party's moderate faction – seven members of which penned a Washington Post op-ed earlier this week backing an impeachment inquiry, the first step in the process.

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Unhappy Republicans are already casting the Democrats' effort as a political scheme to taint a president they failed to defeat in 2016. And a few Republicans are starting to break ranks, with two GOP senators expressing concerns about Trump's behavior and two Republicans governors of blue states saying they back the inquiry announced Tuesday by House Speaker Nancy Pelosi.

"The dam just broke with the Ukraine thing… for Nancy (Pelosi) and everybody else," says Rep. Gerry Connolly, Democrat of Virginia, referring to whistleblower allegations that Trump asked Ukraine to investigate potential 2020 rival Joe Biden and that White House officials covered it up.

"I would say to you confidently that this president will be impeached," Connolly adds. "The timing is the question, and the article or articles of impeachment are the question, but there is no question any longer that he will be impeached."

Pelosi, a liberal California lawmaker, had been reluctant to move in the direction of impeachment over earlier issues, such as alleged obstruction of justice and violation of the federal emoluments clause saying the president cannot accept presents or fees from a foreign government.

Trump, Pelosi explained, wasn't "worth it," given how any impeachment proceeding will divide the nation. Pelosi also needs to worry about the moderates in her caucus, who face re-election races next year in districts Trump won or nearly won.

But the Ukraine matter has changed the dynamics of the impeachment question in less than a week. Support for impeachment, or an inquiry, had grown steadily from fewer than 100 in May to 137 in mid-September, before the Ukraine story broke. But as of Friday, it was at 223 (222 Democrats plus one Independent), with just 13 still listed as undecided.

And one of those holdouts, Rep. Max Rose, Democrat of New York, has gone from being staunchly anti-impeachment to saying this week that "all options must be on the table. "A president attempting to blackmail a foreign government into targeting American citizens is not just another example of scorched earth politics," Rose, who represents New York City's Republican enclave of Staten Island, said in a statement. "It would be an invitation to the enemies of the United States to come after any citizen so long as they happen to disagree with the president."

Republicans say they are united in their defense of Trump, who as president has enjoyed remarkably strong support from Hill GOPers —including those who criticized him when he was a candidate.

"I would say (it's) to the level of almost being overwhelming," says Republican Rep. Chuck Fleischmann, who represents a conservative Tennessee district. Fleishmann said he didn't see the need for further investigation, since he had looked at "all four corners" of the White House's written account of Trump's conversation with Ukrainian President Volodymyr Zelenskiy and "I think there's nothing there."

Rep. Mark Meadows, Republican of North Carolina and chair of the conservative House Freedom Caucus, presaged the party's defense in case Trump is impeached.

The GOP is "resolved in fighting what they see as just another chapter in a political impeachment that started the first day this Congress was sworn in," Meadows says. He dismisses the letter by 300-plus national security officials as a document by "government bureaucrats."

Others are not so full-throated in their defense of Trump. Rep. Greg Walden, an Oregon Republican, declined to talk about the matter, referring a reporter to a written statement he had issued. In that statement, Walden said that while "it wasn't President Trump's finest moment, from what I've seen so far it certainly does not rise to 'high crimes and misdemeanors'."

If all 223 members now on record backing impeachment or an inquiry agree the president has indeed committed "high crimes and misdemeanors," that's enough to impeach, which is essentially an indictment by the House. And early supporters of the move believe that's where it's headed. If the House does impeach, the Senate would be tasked with voting for conviction – something that now appears unlikely, given GOP control of the chamber.

"I think some of these guys are really anxious, because I think they know back home, people are not happy with the latest revelations," says Rep. Jim McGovern, Democrat of Massachusetts.

"When all is said and done, I think there will be some Republicans that will vote with us," adds McGovern, who chairs the powerful House Rules Committee and has served in Congress 22 years. "This is beyond the pale. You can't defend the president on this stuff."

Trump, meanwhile, kept up his usual attack mode, blasting the media, calling anyone who purportedly fed information to the whistleblower a "spy" or "partisan operative," and demanding the resignation of the man at the helm of the inquiry, Intelligence Committee chair Rep. Adam Schiff, Democrat of California.