Clinton said the Iran deal -- which has drawn fierce opposition from Republicans and some Democrats -- is not a step toward normalizing relations with Iran, and she devoted a large portion of her speech at the Brookings Institution to speaking about the need to protect Israel.
Speaking directly to Iran, Clinton said, "The United States will never allow you to acquire a nuclear weapon," adding that she "will not hesitate to take military action if Iran attempts to obtain a nuclear weapon."
The former secretary of state reiterated that she supported the deal because it is a critical part "of a larger strategy toward Iran."
"My approach will be distrust and verify," Clinton said. "We should anticipate that Iran will test the next president."
"That won't work if I am in the White House," Clinton added.
Clinton's speech was full of blunt, tough talk on Iran. She said the country has the "blood of Americans" on its hands, and said she understands "the skepticism so many feel about Iran" due to their "aggression in the Middle East."
"Is (the deal) perfect? Of course not. No agreement like this ever is," Clinton said. "But is it a strong agreement? Yes, it is."
Israel was a key focus for Clinton throughout the speech.
Clinton stressed America's commitment to the Jewish state and promised to continue supporting Israel's military edge over neighboring countries. She also pitched increasing support for Israel's rocket and missile defenses and will back selling Israel more sophisticated aircraft and weapons.
"I wouldn't support his agreement for one second if I thought it put Israel in greater danger," she said. "I know well that the same forces that threaten Israel, threaten the United States. To the people of Israel, you will never have to question whether we are with you. The United States will always be with you."
On domestic policy in Iran, Clinton said she won't rest until every single American citizen detained in the country is brought home. Iran continues to detain three Americans of Iranian background. A fourth American, who was a CIA contractor, remains missing after visiting the country.
She also called for expanding the U.S. military presence in the region, particularly to keep the Strait of Hormuz open, and push to build coalitions to counter Iran proxies like Hezbollah.
Throughout a question-and-answer session, where Clinton was questioned by scholars from the think tank, she subtly claimed she was more hawkish than her former boss, President Barack Obama. On issues like Syria, Russia and Israel, Clinton said cast herself as more forceful.
On Russia's annexation of Crimea, Clinton said, "I am in the category of people who wanted us to do more in response to the annexation of Crimea and the continuing destabilization of Ukraine," a position that puts her at odds with the administration.
Democrats on Tuesday gave Obama the votes he needs to prevent the Senate from passing a measure disapproving of the Iran nuclear deal. Washington Sen. Maria Cantwell, Connecticut Sen. Richard Blumenthal, Michigan Sen. Gary Peters and Oregon Sen. Ron Wyden on Tuesday all announced in rapid-fire succession they would support the deal, giving Obama 42 votes of support in the Senate.
Many Republicans remain against the deal and on Wednesday -- the same day Clinton speaks at the Washington think-tank -- 2016 Republican candidates Donald Trump and Ted Cruz, along with former vice presidential candidate Sarah Palin, will headline a rally on the West Front of the Capitol to express their opposition to the deal.