JEFF ZELENY, ABC NEWS CORRESPONDENT: As the White House sharpens its focus on ISIS, foreign policy is back on the front burner of domestic politics. Republicans are unified in their criticism of President Obama, but they're divided on solutions.
ZELENY (voice-over): Last night in New Hampshire, Senator Ted Cruz sounded the alarm.
SEN. TED CRUZ (R), TEXAS: That this nation literally teeters at the edge of a precipice.
ZELENY: And offered a scolding assessment of how the U.S. is confronting the threat from ISIS.
After bringing GOP activists to their feet, we asked him what he would do.
CRUZ: What we ought to have is a direct concerted overwhelming air campaign to take them out.
ZELENY (on camera): In Iraq and Syria?
CRUZ: The focus should be Iraq, but the real focus should be taking out ISIS. Within Syria, it should not be our objective to try to resolve the civil war in Syria and -- and likewise...
ZELENY: You said that the U.S. should bomb ISIS back into the Stone Age.
Should that take Congressional approval or does the president have the authority to do this on his own?
CRUZ: It should absolutely take Congressional approval, I think.
ZELENY (voice-over): But not all Republicans agree. On Friday, Senator Marco Rubio of Florida sent a letter to the White House saying the president doesn't need Congress, he should act swiftly on his own.
For Republicans eyeing the White House in 2016, early divisions are becoming clear. Senator Rand Paul now says he would destroy ISIS militarily, but his tough talk is at odds with his earlier views, prompting him to write an essay this week in "Time" magazine titled, "I Am Not An Isolationist."
We asked Cruz whether he agreed.
CRUZ: Oh, look, I'm going to let Rand characterize his own views. What I can tell you...
ZELENY (on camera): But he's been...
CRUZ: -- is I will -- I will leave that to Rand and I'll leave that to the American people to make their own judgments.
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ZELENY (voice-over): But among some Republicans, there are growing libertarian views, with deep resistance to another war. Louisiana governor, Bobby Jindal, also visiting New Hampshire, said it was a fine and dangerous line for the party to walk.
GOV. BOBBY JINDAL (R), LOUISIANA: The country, the world needs America to be strong and predictable. The world is getting more dangerous and less predictable because of a lack of American leadership.
ZELENY: ISIS and a long list of foreign policy challenges are already front and center in the warm-up to the 2016 campaign. Positions staked out now likely to become a lasting part of a candidate's record.
So Republicans are trying to keep their comments focusing on criticizing the president, as he prepares to give a speech this week on ISIS.
(on camera): What would you like to hear from him specifically and how urgent is this, most importantly?
CRUZ: I think it is a -- an urgent concern to strike while ISIS is vulnerable.