The Democratic senator described Trump's missive to Turkey's president as "one heck of an interesting letter."
The author responded to the Republican senator's most recent verbal attack on Trump over the president's decision to withdraw U.S. forces from protecting the Kurds in Syria.
"This is a complete and utter national security disaster in the making and I hope President Trump will adjust his thinking," the Republican senator tweeted.
Senate Judiciary Chairman previously made similar remarks during former President Bill Clinton's impeachment hearing.
"We should in a bipartisan way seek to ... change Turkey's behavior," Democratic Representative Eric Swalwell said.
The South Carolina senator and Trump ally slammed the president last week over the withdrawal of U.S. military support in Syria.
"The only way this actually ends is when we protect ourselves against those who would threaten us," Jack Keane said.
"I don't understand how a president that claims he's the toughest President ever would do such a weak move like this," Representative Adam Kinzinger said.
"This is heart-rending for anybody who has shed blood, who has deployed forward," former NATO Supreme Allied Commander James Stavridis said.
The president "recognized that sending American troops to Syria is not in the best national security interest of the United States," Andrew Napolitano said.
Senator Lindsey Graham said back in 1998 that President Richard Nixon's rejection of subpoenas from Congress made him subject to impeachment.
Republicans have sought to pivot the scandal's focus away from Trump's efforts to get other nations' help in the presidential election and are instead focusing on alleged wrongdoing by Joe Biden and his son.
"We are voluntarily abdicating our role and it's the Russians, Iranians and others who are benefitting," Richard Haass warned.
"I am absolutely appalled that the United States is going to betray those Democratic forces in northern Syria," Pat Robertson said on "The 700 Club."
"By abandoning the Kurds we have sent the most dangerous signal possible – America is an unreliable ally," the Republican senator from South Carolina argued.
The campaign of Jaime Harrison announced that the first-time Senate candidate "brought in more quarterly money than any other South Carolina Democratic Senate challenger in history."
South Carolina senator told The Sean Hannity Show that Attorney General should be speaking with foreign leaders about the Mueller inquiry.
"It is a betrayal of the office at the scale of which I haven't seen in my lifetime," the Democratic presidential candidate and senator said.
President Donald Trump should "tell us as much as he can, without compromising executive privilege, so that we can understand what happened," the South Carolina Republican told a conservative radio host.
The South Carolina Republican is unfazed by the Inspector General's probe into the Hurricane Dorian forecast debacle around President Donald Trump and Commerce Secretary Wilbur Ross.
The pair were attending the Ambrosetti Forum in Italy's Lake Como on Saturday.
"Here's a scenario that I think is real: there's a hurricane, a natural disaster, no power, no cops, no anything," the Trump ally said. "I think if you show up on the porch with an AR-15, they'll probably go down the street."
"This is what 2020 is about. If we can get the House back and keep our majority in the Senate, and President Trump wins re-election, I can promise you not only are we going to repeal Obamacare, we're going to do it in a smart way..."
President Donald Trump is reportedly considering tougher background checks on gun purchases but faces Republican opposition to meaningful reform.
Broadway star Patti LuPone attacked Republican Senator Lindsey Graham on Twitter, calling him a "disgrace" and suggesting he was in the closet.
"I don't think it's racist to say," Graham said. "What this is about to me is that these four congresswoman, in their own way, have been incredibly provocative."
"They hate Israel, they hate our own country, they're calling the guards along our border—the border patrol agents—concentration camp guards," the South Carolina Republican said on Fox and Friends.
Lindsey Graham said it is "so easy" for terrorists from the Middle East to join up with Central American migrants and cross through Mexico and the U.S. southern border.
"We need to reevaluate our long-term relationship with Saudi Arabia," Republican Senator John Barasso said.
Democrat Jaime Harrison has raised a record-breaking $1.3 million over the last three months for his fight against Graham for the Senate seat next year.