"It's my belief that if you're Bashar al-Assad and you read that it is no longer a priority of the United States to have you removed from power — I believe that that is an incentive to act with impunity," Rubio, the junior Florida senator, said at a news conference today.
He added, "I personally do not believe that it's coincidental."
Tillerson said last week during a press availability in Turkey, "The longer-term status of President Assad will be decided by the Syrian people."
Rubio said he doesn't believe Tillerson thought Assad would take advantage of his remarks by carrying out a chemical attack, as he did this week, reportedly leaving at least 72 civilians dead.
The senator also said he thought Assad likely would have carried out the attack regardless of what, if anything, the Trump administration said.
The White House did not immediately respond to ABC News' request for comment.
"We need to get him indicted," Cardin said.
Rubio was asked during the news conference about Trump's statement in reaction to the Syrian attack, in which he said, "President Obama said in 2012 that he would establish a 'red line' against the use of chemical weapons and then did nothing."
Rubio said, "That presidency's over. We have a new presidency."
"Any effort to take any iota of blame away from the people truly responsible does not further the cause that we seek to make and bring light to today," Rubio said.