(CNN) President Donald Trump spent most of Monday defending his choice to stand down in Syria after a weekend spent on Twitter making claims about former Vice President Joe Biden, Democratic critics and the whistleblower whose report sparked the impeachment inquiry.
Here's the latest on the historic investigation:
The main question, as Democrats move toward impeachment in the House, is whether the Republican-controlled Senate will close ranks around President Donald Trump -- or not.
CNN's Ted Barrett, Haley Byrd, Manu Raju, Sunlen Serfaty, Alex Rogers and Clare Foran have contacted more than 80 offices for Republican lawmakers in the House and Senate in recent days to ask for a response to Trump's remarkable public call for foreign governments to investigate former Vice President Joe Biden and his son Hunter.
From their report:
Only a few responded; just a handful have expressed any misgivings to CNN or other outlets.
... Why the silence? Trump holds powerful sway over congressional Republicans, largely because he is wildly popular with the same Republican voters who will decide whether to reelect these lawmakers. Most who defy Trump end up out of office, about the last place any politician wants to be.
"The President should not have raised the Biden issue on that call, period. It's not appropriate for a president to engage a foreign government in an investigation of a political opponent," Sen. Rob Portman of Ohio told the Columbus Dispatch.
Along with a few other statements critical of Trump over the weekend and last week from Sens. Mitt Romney, Ben Sasse and Susan Collins, that's the beginnings of at least a small foundational crack in GOP support for Trump.
But there's a big difference between criticism and opposition. Indeed, Portman told the Dispatch of Trump's behavior, "I don't view it as an impeachable offense."
And he also said, "I think the House frankly rushed to impeachment assuming certain things," according to the paper.
It's not that Senate Republicans are afraid to disagree with Trump on everything.
Sen. Lindsey Graham of South Carolina has gone nearly apoplectic against Trump over Syria and called Trump's move to pull US troops and allow Turkey space to move in "shortsighted and irresponsible."
It was a surprising turnaround for a former Trump critic who's emerged as a key Senate ally, as well as a frequent golf partner. On the impeachment inquiry Graham has achieved status as presidential defender no. 1 against the whistleblower.
Also Monday, Senate Majority Leader Mitch McConnell said in a statement directed at Trump that there's a veto-proof majority in the Senate that disagrees with him.
But that willingness to stand up to Trump on Syria makes the failure to call Trump out over his public calls for foreign interference in US elections more jarring.
McConnell also has a new TV ad in which he paints himself as the one person who can save Trump's presidency.
House investigators had hoped for multiple depositions this week, but they may only get one (behind closed doors).
US Ambassador to the EU Gordon Sondland did not appear on Tuesday after the State Department blocked his testimony.
Why he's important:
Former US Ambassador to the Ukraine Marie Yovanovitch is supposed to testify on Friday. After Sondland was kept from testifying, it will be interesting to see if Yovanovitch shows.
Why she's important:
Three key allies of Giuliani and two State Department officials likely won't testify this week before the impeachment inquiry. The committee has threatened subpoenas for Giuliani's associates.
Lev Parnas and Igor Fruman, associates of Giuliani
Why they're important:
Semyon "Sam" Kislin
Why he's important:
Ulrich Brechbuhl, Counselor of the State Department
Deputy Assistant Secretary of State George Kent
Why he's important:
From CNN's Kylie Atwood: Most of the text messages that Kurt Volker turned over to the congressional committees conducting the impeachment inquiry last week were carried out over WhatsApp, according to two sources. When Volker handed them over to the committees he simultaneously handed the same documents over to the State Department for record keeping purposes, explained one of the sources familiar with his actions. There are still some additional messages that Volker will hand over to State in the coming weeks, which are not relevant to the inquiry.
Federal record keeping requires all government employees to turn over official copies of any electronic messaging to the agencies they work for no later than 20 days after it was created. Volker did not turn over some of these messages in time to meet that deadline. The State Department did not reply to multiple questions from CNN.
CNN's Manu Raju and Zachary Cohen report on a list of ideas the House Democrats have to protect the identity of the whistleblower, who is in the unusual position of having been openly targeted by the President of the United States:
Democrats are not unanimous in their support of the impeachment inquiry. CNN's Aaron Kessler looked at what the 8 have in common.
What's below is from his report, which has maps and charts to drive these points home, but it is worth mentioning that these types of members are why Democrats have the majority:
Trump country
Slim margins
Demographics
Trump downsizes National Security Council -- The President has ordered a substantial reduction in the staff of the NSC, according to Bloomberg. It's not clear if the cuts come as a result of the whistleblower complaint. LINK
Kurt Volker officially resigned from McCain Institute -- CNN had reported last week he was planning to leave (CNN)
Perry speaks again -- Rick Perry said again Monday that he "asked the President multiple times" to call Zelensky. But Perry said he was encouraging talks about energy, not the Bidens. How does this help Trump since his ultimate talk with Zelensky ended up focused on investigations into the Bidens and the 2016 election? (CNN).
CNN's Daniel Dale fact checks all things Trump and he had several opportunities over the weekend. Here's one:
Trump tweeted Sunday of Biden: "Sleepy Joe said he never spoke to the Ukrainian company, and then the picture came out where he was playing golf with the company boss and Hunter ..."
Facts First: The photo Trump appears to be referencing does not show Joe Biden playing golf with the "company boss" of Burisma Holdings, the Ukrainian natural gas company where his son Hunter Biden was a board member. The person in the photo is an American named Devon Archer, a longtime business associate of Hunter Biden who has also served on the Burisma board. A board member is not the "company boss" -- nor an "exec," as a previous Trump tweet had identified Archer.
The fourth person in the photo with Archer and the Bidens has not been publicly identified, but he is not Burisma owner Mykola Zlochevsky or top executive Taras Burdeinyi.
The President has invited foreign powers to interfere in the US presidential election.
Democrats want to impeach him for it.
It is a crossroads for the American system of government as the President tries to change what's acceptable for US politicians. This newsletter will focus on this consequential moment in US history. Let us know what you think by dropping us a line at impeachment@cnn.com.