Israeli Prime Minister Benjamin Netanyahu waves as he speaks before a joint meeting of Congress on Capitol Hill in Washington on Tuesday. Netanyahu warned the U.S. against an emerging nuclear agreement with Iran.

WASHINGTON — In a direct challenge to the White House, Israeli Prime Minister Benjamin Netanyahu stood before Congress on Tuesday and warned the U.S. that an emerging nuclear agreement with Iran “paves Iran’s path to the bomb.” President Barack Obama pushed back sternly, saying the U.S. would never sign such a deal and Netanyahu was offering no useful alternative.

In the U.S. spotlight for a day, the Israeli leader showed no uncertainty. “This is a bad deal. It is a very bad deal. We are better off without it,” he declared in an emotionally charged speech that was arranged by Republicans, aggravated his already-strained relations with Obama and gambled with the long-standing bipartisan congressional support for Israel.

Two weeks ahead of voting in his re-election in Israel, Netanyahu took the podium of the U.S. House to say any nuclear deal with Iran could threaten his nation’s survival.

In a tone of disbelief, he said Iran’s supreme leader, Ayatollah Khamenei, “tweets that Israel must be annihilated — he tweets.”

Republicans loudly cheered Netanyahu in the packed chamber, repeatedly standing. Democrats were more restrained, frustrated with the effort to undercut Obama’s negotiations. House Minority Leader Nancy Pelosi, D-Calif., did little to hide her unease and later issued a blistering statement criticizing what she called Netanyahu’s condescension.

At the White House, Obama said there was value in the current economic sanctions against Iran and also in the negotiations in Switzerland aimed at restraining Iran’s nuclear ambitions.

“Sanctions alone are not sufficient,” Obama said. “If Iran does not have some sense that sanctions will be removed, it will not have an interest in avoiding the path that it’s currently on.”

The administration says there is no deal yet, but Netanyahu insists he is privy to what is being put forth.

“If the deal now being negotiated is accepted by Iran, that deal will not prevent Iran from developing nuclear weapons. It would all but guarantee that Iran gets those weapons — lots of them,” he declared.

Obama declined to meet with the leader of Israel, a key U.S. ally, during this visit. Vice President Joe Biden was on a trip to Central America and so his seat as president of the Senate was filled by Republican Orrin Hatch of Utah, the Senate president pro tempore.