Congress is sending a clear message to President Donald Trump that he will face strong resistance should he fire Special Counsel Robert Mueller. Contained in that message is a second — the president wouldn't get away with trying to block justice.

Before legislators depart for summer break, the Republican-controlled Senate used a procedural move to block a recess appointment, clearly aimed at preventing the president from firing Attorney General Jeff Sessions and appointing a successor without confirmation by the Senate. A Republican-controlled Senate first used the procedural move against President Barack Obama, scheduling brief meetings every few days so the Senate is technically not in recess.

Firing Sessions could be a first step in a move to rid the Trump administration of Mueller. And though Trump has ceased his attacks on his own attorney general — this week praising him for a planned crackdown on those responsible for leaking classified information to the media — some in Congress know dramatic shifts by Trump are to be expected and must be guarded against.

Also last week, two sets of senators offered different versions of legislation aimed at preventing the president from firing Mueller and truncating his investigation.

Republican Lindsey Graham of South Carolina and Democrat Cory Booker of New Jersey introduced a bill that would require a panel of judges to review a proposed firing before it could take effect. The president would have to show just cause for the removal.

A second proposal by Sen. Thom Tillis, R-North Carolina, and Christopher Coons, D-Delaware, would give the special counsel the right to contest his removal in court, which would have two weeks to determine if the firing had merit or should be reversed.

U.S. Sen. Richard Blumenthal of Connecticut, who backed the Graham-Booker proposal and appeared on a cable TV news outlet to talk about it, was the target of a Trump bullying effort Monday. Again repeating an issue first raised during Blumenthal's initial run for Senate in 2010, the president tweeted it was "interesting" to watch Blumenthal "talking about hoax Russian collusion when he was a phony Vietnam con artist!"

In 2010, videos emerged of Blumenthal referencing himself as a Vietnam veteran. While he served as a Marine Corps reservist during that war, he did not serve in Vietnam. During the 2010 campaign, Blumenthal offered an emotional apology. Trump, known for his resistance to apologizing, dismissed Blumenthal's prior actions as having "cried like a baby and begged forgiveness like a child."

While Blumenthal certainly erred in exaggerating his service, Trump's crude criticism of the senator is loathsome and immature. Trump did not serve. He received four draft deferments while attending college. When Trump became eligible for the draft in 1968, a doctor diagnosed the former multi-sport athlete with bone spurs in his heels, keeping him out of the draft and Vietnam.

Later asked about the medical issue, for which he never received treatment, Trump explained, "Over a period of time, it healed up."

And, by the way, Russian interference in the 2016 election is not a hoax. Currently two grand juries are in place, allowing Mueller and his team of lawyers to gain the testimony and subpoena the documents necessary to uncover any criminal wrongdoing. Potential targets include collusion with Russia's interference in the election, efforts to obstruct the investigation, or questionable financial activities and other relations with Russians that might leave the administration vulnerable to coercion.

Under the regulations governing Mueller's investigation, he can only be removed by the attorney general, but in this case Attorney General Sessions has recused himself from the matter because of his role in the Trump campaign and meetings with a Russian official. That would leave it to Deputy Attorney General Rod Rosenstein, who appointed Mueller and said he has no intention of halting the investigation. But if Trump appointed a new attorney general, he or she could fire the special counsel.

Or Trump could move to fire Mueller directly, arguing that as president he does not have to follow Department of Justice regulations.

One would expect Trump to only make such moves if he felt Mueller was close to incriminating him or someone near to him. Some in Congress recognize they cannot let that happen, if need be passing a law to keep Mueller and his investigation in place. Constitutional crisis would not be too strong a phrase in such a situation. It would be a sad day for the nation if it ever came to that but the possibility can no longer be viewed as remote.

The Day editorial board meets with political, business and community leaders to formulate editorial viewpoints. It is composed of President and Publisher Timothy Dwyer, Executive Editor Izaskun E. Larraneta, Owen Poole, copy editor, and Lisa McGinley, retired deputy managing editor. The board operates independently from The Day newsroom.