WASHINGTON (Reuters) - Republican presidential front-runner Donald Trump on Monday vowed an unbreakable U.S. alliance with Israel if he is elected president in November, seeking to clear up confusion over his repeated pledges to remain neutral in any peace negotiations between Israelis and Palestinians.

Trump’s speech to the American Israel Public Affairs Committee, a powerful pro-Israel lobbying group, was part of a daylong effort by the anti-Washington candidate to persuade establishment Republicans to get behind his insurgent candidacy and give up on an effort to deny him the party’s presidential nomination.

Describing Israel as ready to negotiate a peace agreement, Trump said the Palestinians would have to be willing to accept that Israel will forever exist as a Jewish state and able to stop attacks on Israelis.

“The Palestinians must come to the table knowing that the bond between the United States and Israel is unbreakable,” the New York billionaire businessman said.

Trump has drawn fire for his position on Middle East peace negotiations. He has described himself as extremely pro-Israel, but has said he would take a “neutral” stance in trying to negotiate an elusive peace settlement between Israel and the Palestinians.

Trump’s critics have said he could harm long-standing U.S. support for Israel. Trump’s leading Republican rival, U.S. Senator Ted Cruz, reminded the AIPAC gathering of Trump’s position.

“Let me be very, very clear,” Cruz said. “As president I will not be neutral. America will stand unapologetically with the nation of Israel.”

Democratic presidential front-runner Hillary Clinton, a former secretary of state, used her AIPAC appearance to attack Trump.

“We need steady hands, not a president who says he’s neutral on Monday, pro-Israel on Tuesday and who-knows-what on Wednesday because everything’s negotiable,” she said.

Clinton also took aim at Trump’s vow that, if elected, he would deport illegal immigrants and bar Muslims temporarily from entering the United States.

“If you see bigotry, oppose it, if you see violence, condemn it, if you see a bully, stand up to him,” she said.

TRUMP TELLS PEOPLE: “BE SMART”

In a rarity, Trump delivered his AIPAC speech with the aid of a TelePrompter, abandoning his typical free-wheeling style. Throughout the day, his public remarks lacked their usual bombast, an obvious effort to appear more presidential.

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At a news conference, Trump presented himself as Republicans’ best chances of capturing the White House in the Nov. 8 election. He took steps to appear as the nominee-in-waiting, releasing the names of some foreign policy advisers and pledging to name seven to 10 people he would pick for the Supreme Court.

Trump said establishment Republicans would be making a mistake if they persuade a high-profile party leader to launch a third-party run to deny him the White House. He said it would “almost certainly” mean the Democrats would win the presidency.

“If people want to be smart, they should embrace this movement,” Trump said at the site of a new hotel he is building in Washington. “If they don’t want to be smart, they should do what they’re doing now and the Republicans are going to go down to a massive loss.”

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Trump laid out some foreign policy priorities in a CNN interview, saying the United States is contributing more than it should to the NATO alliance and that he would continue a U.S. thaw toward Cuba begun by President Barack Obama, who is now in Havana.

Trump was in Washington for closed-door talks with a variety of Republicans organized by his top backer in the capital, U.S. Senator Jeff Sessions of Alabama. It was his most overt bid yet to seek party unity at a time when many establishment Republicans bitterly oppose him.

The meeting, held at the offices of the Jones Day law firm, included some Republican lawmakers and a former Republican speaker of the U.S. House of Representatives, Newt Gingrich, and former Congressman Bob Livingston.

“We’ve had almost eight years of Mr. Obama, who’s been a disastrous president. We have now an opportunity to change course or have four more years of the same. And I think that Donald Trump is the alternative,” Livingston said after the session.

Also at the meeting were Representatives Renee Ellmers of North Carolina and Chris Collins of New York, as well as former Senator Jim DeMint, who is head of the Heritage Foundation, an influential conservative Washington think-tank.

In a separate session with the Washington Post editorial board, Trump named some members of his foreign policy team.

The team included Walid Phares, who Trump called a counter-terrorism expert; George Papadopoulos, an oil and energy consultant; and Joe Schmitz, a former inspector general at the Department of Defense.

Trump’s rise has alarmed establishment Republicans who have tried in vain to stop him. Their best hope of derailing his insurgent candidacy is to stretch the contest out and deny him the 1,237 delegates needed to formally win the party’s presidential nomination.

Trump has 678 delegates to 423 for Cruz and 143 for Ohio Governor John Kasich, according to the Associated Press.

If Trump does not win the 1,237 delegates, the Republican nominee would be decided at the party’s convention in Cleveland in July.