(CNN) Washington's impeachment battle over President Donald Trump's conduct with Ukraine is intensifying with news of a second whistleblower while new testimony this week brings the prospect of more stunning revelations to deepen the crisis.

Yet nearly all Republicans, taking advantage of a congressional recess, are staying silent despite more and more evidence that the President used his power to pressure a foreign nation for personal political gain.

Most of the few Republicans who have broken cover are struggling to come up with a logical defense of the President's actions — but his grip on the GOP is evident in the unwillingness of most to criticize him. And the President's assault on former GOP nominee and Utah Sen. Mitt Romney -- who he branded as a "pompous 'ass'" is underscoring the price Republicans will pay for rebuking the commander in chief.

Trump is meanwhile hyping rallies this week in Minnesota and Louisiana that are likely to stress his powerful support among his base and will hike new pressure on any wavering Republicans before most of them return to Washington next week.

The weekend's political exchanges suggested that despite a week of barely believable drama, Trump's feverish efforts are having some success in stopping any serious slippage in support among Republican lawmakers, especially ahead of any eventual Senate impeachment trial.

But recent developments also sharpen the core questions at stake in the impeachment saga that are critical to the office of the presidency going forward and US democracy itself.

Given the evidence that is already public, the question is becoming — is it permissible for a President to use his power, sometimes even in public — to pressure foreign governments to investigate political opponents before an election?

There is a sense that the history with which future generations will judge today's leaders is being written every day.

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Second whistleblower brings new intrigue

The biggest development over the weekend came with the revelation that lawyers for the intelligence official that set off the impeachment fight are acting for a second whistleblower

Attorney Mark Zaid told CNN that the person works in the intelligence community and has first-hand knowledge that supports claims made by the first whistleblower.

The initial complaint alleges that Trump abused his power to urge a foreign nation — Ukraine — to investigate a domestic opponent — Joe Biden — and that the White House covered it up.

The new whistleblower could potentially blow a hole in the key GOP defense — that his or her predecessor only had second-hand knowledge of the conduct that could lead to Trump's impeachment.

Trump responded quickly to the potential threat of a second whistleblower, part of a weekend of frenetic tweeting that mostly involved often misleading accounts on conservative media.

"The first so-called second hand information "Whistleblower" got my phone conversation almost completely wrong, so now (sp) word is they are going to the bench and another "Whistleblower" is coming in from the Deep State, also with second hand info," the President wrote on Saturday night.

After new details of the second official coming forward dominated Sunday news shows, White House spokeswoman Stephanie Grisham insisted nothing had changed.

"It doesn't matter how many people decide to call themselves whistleblowers about the same telephone call — a call the President already made public — it doesn't change the fact that he has done nothing wrong," Grisham said Sunday afternoon.

On Sunday, a group of 90 former national security officials who served under both Democratic and Republican administrations signed an open letter praising the whistleblower for following the appropriate legal channels, and calling on the government and the media to protect the whistleblower's identity, according to the Wall Street Journal

The White House defense therefore rests in trying to convince voters that the transcript of the phone call between Trump and Ukrainian President Volodymyr Zelensky does not show what in fact is clear — that he asked Ukraine for "a favor" immediately after a discussion of future military aid.

Text messages between key US officials released late Thursday also appear to bolster the case that there was a quid pro quo that suggests Trump saw concessions to Ukraine as contingent on probes into Biden and conspiracy theories that it, not Russia, was the origin of 2016 election meddling.

Republicans dance on pin heads

The extreme political test posed to Republican lawmakers by the impeachment saga was on display on Sunday talk shows.

Trump made multiple attacks on Romney , apparently seeking to ensure the former Republican nominee's vigorous criticisms of presidential conduct did not spread in the GOP.

But another lawmaker from Utah, Rep. Chris Stewart accused Democrats of being "giddy" about impeachment.

"Three years they've been trying to impeach this President. Three years they've been looking for reasons to remove him from office. They're not pained by this," he said on Fox News Sunday.

"It's terribly divisive for the American people."

Maine Sen. Susan Collins is one of the Republicans up for reelection in 2016 who must fret about the party's pro-Trump base and more moderate voters in a general election.

Her rhetorical gyrations encapsulated her plight.

"I thought the President made a big mistake by asking China to get involved in investigating a political opponent," Collins was quoted as saying on Saturday by the Bangor Daily News . "It's completely inappropriate."

But Collins also associated herself with conservative arguments that the impeachment probe is too partisan.

She said she was concerned that House Intelligence Committee chairman Adam Schiff "misrepresented and misled people" about the content of the Zelensky-Trump call on July 25.

"I hope this will be done with the seriousness that any impeachment proceeding deserves," Collins said, according to WABI television.

Lawmakers like Collins will come under searing pressure next week when most lawmakers will be back in town and it will be harder for them to dodge questions about events in the past few days -- and the tumbling revelations that have marked the Ukraine scandal.

Democrats bemoan GOP 'blind partisan loyalty'

The White House did not provide any officials or members of Trump's legal team to make his case on the talk shows.

Democratic Rep. Jim Himes of Connecticut suggested that the emergence of a second whistleblower suggested that the walls around Trump were beginning to crumble.

"People around the President, professional (people) who are in the Oval Office, who are in the Situation Room, are watching what is happening and are finally saying 'My God, this cannot happen anymore and they are coming forward," Himes said on CBS "Face the Nation."

Another member of the Nutmeg State's congressional delegation, Sen. Chris Murphy, bemoaned how Republicans are lining up behind Trump, despite the gravity of allegations against him.

I am deeply scared by the positioning that Republicans have chosen to take," Murphy said on NBC's "Meet the Press." "This entire country should be scared that in a moment when we need patriots, what we are getting is blind partisan loyalty."

The House and Senate observe the second half of a two-week recess this week. But the Democratic impeachment investigation will speed ahead.

On Tuesday, US Ambassador to the European Union Gordon Sondland is expected to attend a closed-door deposition with three key House committees.

Sondland was included on a series of text messages that show how a potential Ukrainian investigation into the 2016 election was linked to a desired meeting between Zelensky and Trump.