"When the United States says it is unacceptable for Iran to have a nuclear weapon, we mean what we say," President Obama tells The Atlantic.

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hen it comes to destroying Iran's nuclear program, President Obama says all options, including military force, are on the table. "I don't bluff," he tells The Atlantic. "When the United States says it is unacceptable for Iran to have a nuclear weapon, we mean what we say." Obama's comments constitute "the most direct threat he has issued during months of escalating tension" between Iran and the U.S., says Anne Gernan at the Associated Press. And the tough talk comes just as Obama is about to host Israeli Prime Minister Benjamin Netanyahu at the White House Monday. What exactly is motivating Obama's hawkish tone? Here, three theories:

1. He needs to emphasize that he has Israel's back
Obama's critics constantly claim that he is a lousy friend to Israel, and even some of his Democratic "supporters are concerned about" his commitment to the U.S.'s longtime ally, says Christi Parons at the Los Angeles Times. That's why Obama made a point of saying he "has Israel's back." Americans "instinctively sympathize with Israel," the president said. So "why is that despite me never failing to support Israel on every single problem that they've had over the last three years, that there are still questions about that?"

2. But he also wants Israel to back off Iran
Israeli officials have been hinting at a pre-emptive strike against Iranian nuclear facilities for weeks. The White House has long appeared reluctant about backing such a military operation, leaving Obama with the challenge of delivering "two competing messages," says Ethan Bronner in The New York Times. He must join Israel in "warning Iran to abandon its nuclear program or face military action," while also convincing Israel to allow newly imposed sanctions to take effect before launching a strike. In his interview with The Atlantic, Obama seemed not only to support Israel, but to pressure them too, talking up the sanctions by saying they had put Iran "in a world of hurt," and might lead Tehran to reconsider its nuclear program out of "strategic calculation."

3. GOP presidential candidates are dragging Obama right
The contest for the GOP presidential nomination is having a growing impact on Obama's foreign policy, with the candidates assailing him for supposedly being weak-kneed in the face of the Iranian threat. Because of that, the president almost has to sound hawkish. "Obama cannot afford to be too tough on Netanyahu, with Republican presidential candidates ready to pounce on any sign of a rift" between the two leaders, write Matt Spetalnick and Jeffrey Heller at Reuters. The constraints of the November election leave Obama "with somewhat less room to maneuver than he would have at another moment in his presidency," says Bronner.