GWEN IFILL: Presidential politics came to Capitol Hill today, as Republican candidates joined with lawmakers to protest the Iran nuclear deal.
Political director Lisa Desjardins was there.
SEN. TED CRUZ, Republican Presidential Candidate: God bless the United States of America.
LISA DESJARDINS: Republican presidential hopefuls and rivals Donald Trump and Ted Cruz joined forces to slam the nuclear deal with Iran.
SEN. TED CRUZ: Let's rise up and tell every elected official in Washington, no more talk, no more show votes. Get it done. Stop this deal!
LISA DESJARDINS: Thousands gathered on the west lawn of the U.S. Capitol to hear the speeches, many using umbrellas for shade in the 90-degree Washington heat.
WOMAN: If this deal goes through, I'm really scared for our country.
FRED GORDON, Rally attendee: I don't like the Iran deal. And I think it's going to hurt us in the long run.
LISA DESJARDINS: The Texas senator organized the event, along with Tea Party supporters, but the star of the show was clear.
DONALD TRUMP, Republican Presidential Candidate: Never, ever, ever in my life have I seen any transaction so incompetently negotiated as our deal in Iran. And I mean never.
LISA DESJARDINS: Hours earlier, inside the Capitol, Secretary of State John Kerry dismissed much of the opposition as irrelevant.
JOHN KERRY, Secretary of State: I believe that the people who count are the 42 senators who have made up their minds. That's the count that matters right now. And if Donald Trump and Ted Cruz and Dick Cheney want to be the face of the opposition, that's their choice.
LISA DESJARDINS: The 42 senators are Democrats who support the deal and could block any Republican move to disapprove it. With that in mind, Kerry and Energy Secretary Ernest Moniz sought to pressure Republicans to move on.
JOHN KERRY: We hope that the Senate would move rapidly to do the business of our country, not of a party, but the business of our nation.
LISA DESJARDINS: But all the words and all the drama inside the U.S. Capitol today likely will not change the legislative fate of the Iran deal. President Obama has more than enough votes for it to survive in the U.S. Senate.
But the rally outside and other words today may indicate the real future of the Iran deal, as a hot issue for 2016. Democratic hopeful Hillary Clinton laid out her views in a Washington speech. She acknowledged that the Iran deal is not perfect, but maintained it's the only way to keep Iran from developing a nuclear bomb.
HILLARY RODHAM CLINTON, Democratic Presidential Candidate: Either we move forward on the path of diplomacy and seize this chance to block Iran's path to a nuclear weapon, or we turn down a more dangerous path, leading to a far less certain and riskier future.
LISA DESJARDINS: And on the Senate floor, her Democratic rival Bernie Sanders compared critics of the deal to those who voted to go war with Iraq in 2003.
SEN. BERNIE SANDERS, Democratic Presidential Candidate: Unfortunately, these individuals have learned nothing from the results of that disastrous policy and how it destabilized that entire region.
LISA DESJARDINS: The Iran deal seems certain to figure again in the next Republican presidential debate. That's a week from now. The deadline for Congress to vote is the next day.
Lisa Desjardins, PBS NewsHour, Washington.