Sen. Ted Cruz, R-Texas, on Sunday said a U.S. strike on Syria would be a “mistake” and charged that the Obama administration had no “viable plan for success.”

“A military attack is a mistake,” said Cruz on ABC’s “This Week.”

“This attack is not based on defending U.S. national security,” he added.

President Obama has asked Congress to authorize a military strike on Syria to punish strongman Bashar Assad for using chemical weapons in that country’s two-year civil war. But that call faces an uphill climb with liberal Democrats and conservative Republicans both skeptical of U.S. intervention.

The White House though is making a full-court press to rally support with Obama to deliver a national address on Tuesday, arguing that U.S. credibility is at stake after Assad crossed a “red line” by using weapons of mass destruction. Chief of Staff Denis McDonough appeared on all five Sunday shows to make the administration’s case that Assad should be punished.

McDonough also criticized Cruz for comments the Texas senator made last week arguing that the U.S. would be acting as “al Qaeda’s air force” if they intervened. Many of the Syrian rebel groups seeking Assad’s ouster are Islamist, leading to concerns that anti-Western elements could be boosted by a U.S. strike.

McDonough said he was “outraged” by Cruz’s remarks, but the senator defended his comments on Sunday.

“There is a lot to be outraged about. All of us are outraged by Assad’s conduct,” said Cruz calling him a “brutal murderer.” “He rightly should be subject to condemnation.”

But he added that Obama is “proceeding with the wrong objective.”

The strike “is explicitly framed by President Obama, Secretary [of State John] Kerry as a defense of what they call international norms and I don’t think that’s the job of our military to be defending international norms,” said Cruz.

The senator said he would take other steps to isolate Assad including pressing Iraq to block Iranian flights resupplying the Syrian regime from flying over their airspace.

The White House has declined to say if Obama would act if Congress fails to back him, saying they are confident lawmakers will back a military response.

Cruz Sunday said Obama had “no authority to act” if Congress failed to provide authorization.