"Get ready Russia, because they will be coming, nice and new and “smart!”" Mr. Trump tweeted.
On Capitol Hill, Defense Secretary James Mattis sidestepped any details of possible plans, as he was asked about Syria repeatedly at a House hearing.
"I do not want to discuss the current situation, because I owe confidentiality to our allies," Mattis said, as the Pentagon chief acknowledged the difficulty in dealing not only with Syria, but Russia as well.
"On a strategic level, it's how do we keep this from escalating out of control," Mattis said. "If you get my drift on that."
On Monday, the President vowed that military decisions on a Syria strike would be made within 24 to 48 hours, as the White House scrapped his planned trip to South America next week to allow him to deal with the Syrian crisis.
That was followed by yesterday's tweet about missiles and Russia.
Democrats in Congress said the tweets demonstrated the Trump Administration wasn't ready for prime time, as Sen. Robert Menendez (D-NJ) called Mr. Trump the "Commander-in-Chaos."
"This is the most solemn and serious decision a President must make, and it’s never been done in such a disorganized and juvenile manner," said Sen. Brian Schatz (D-HI).
There were also a few voices in both parties who called on the President to get the permission of Congress before launching any strike.
"We can’t bomb our way to peace," said Rep. Barbara Lee (D-CA).
"I again implore President Trump to consult with Congress before engaging our armed forces," said Sen. Mike Lee (R-UT).
Those two Lees are not related - and are on opposite sides of the political spectrum - but they represent a small slice of the House and Senate who feel Congress is too often left out of decisions on using U.S. military force.