Washington (CNN) After years of tensions between President Barack Obama and segments of the pro-Israel community, would-be successor Hillary Clinton is taking steps to reassure voters of her stalwart support for Israel.

Clinton, the frontrunner for the Democratic presidential nomination, last week sent letters to several top Jewish donors and community leaders expressing her staunch opposition to calls to boycott Israel and her hope to work with the recipients to fight attempts to isolate Israel, according to copies obtained by CNN.

The letter comes as pro-Israel activists and donors are increasingly alarmed that the boycott movement, which has swept through several European legislatures, is now gaining a foothold in the U.S. -- and as Republican presidential candidates are trying to seize on strains between the Obama administration and Israeli government to outflank Democrats on their support for Israel.

In the latest flare-up, the State Department released a statement criticizing a recently passed trade bill amendment -- seeking to prevent U.S. trading partners from joining Israel boycotts -- that raised concerns among many pro-Israel advocates of the Obama administration's commitment to countering the boycott calls.

Though supportive of efforts to stop the boycott movement, known as BDS, the statement objected to the amendment's language for not distinguishing between Israel and "Israeli-controlled territories," i.e. the West Bank.

The bulk of the BDS movement targets all of Israel, but some activists only seek to prevent trade with Israeli settlements in the West Bank.

"By conflating Israel and 'Israeli-controlled territories,' a provision of the Trade Promotion Authority legislation runs counter to longstanding U.S. policy towards the occupied territories," State Department Spokesman John Kirby said in the statement, pointing to U.S. opposition to settlements.

Obama signed the legislation despite the State Department statement, which was issued one day after the bill became law. But several American Jewish leaders were still troubled by the statement.

"I found it very disturbing and inappropriate," said Malcolm Hoenlein, executive vice chairman of the Conference of Presidents of Major Jewish Organizations.

He said the anti-boycott amendment in the trade legislation clearly had nothing to do with the U.S. policy opposing settlement activity and suggested he's not completely confident the Obama administration would play defense for Israel if a boycott targeted only at Israeli settlements came up.

Some in the Jewish community are wondering whether this is a sign of the White House making good on threats to back away from its staunch support of Israel in international forums after Israeli Prime Minister Benjamin Netanyahu's controversial comments during his election campaign this spring.

In the final days of the race, Netanyahu publicly wavered on his commitment to achieving a two-state solution and made incendiary comments about Arab voters -- on the heels of an address to Congress in which he railed against U.S. policy on Iran in defiance of the White House.

Afterward, Obama told Netanyahu the U.S. would have to "reassess" aspects of its relationship.

The Obama administration, however, insisted that its statement was simply intended to clarify U.S. settlement policy. "Nothing's changed about our policy of not supporting boycotts of the State of Israel," Kirby said at a briefing last week.

Beyond the boycott issue, the Netanyahu-Obama tensions have raised the prospect of the U.S. taking a stance at the U.N. less to Israel's liking.

A major test of this shift is expected this fall, when the French government is due to present a plan at the U.N. that -- if the U.S. abstains from using its veto -- would impose a timeline on Israel and the Palestinians to negotiate a two-state solution to their decades-old conflict, a measure Israel strongly opposes.

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That may be why Clinton also noted in her letter that a peaceful resolution "can only be achieved through direct negotiations between Israelis and Palestinians -- it cannot be imposed from the outside or by unilateral actions."

"She's coming very close to saying, 'I will not support the French initiative at the Security Council,'" said David Makovsky, who worked on the Israeli-Palestinian conflict at the State Department following Clinton's departure and is now with the Washington Institute for Near East Policy.

Clinton could be sending a signal to the Obama administration, Makovsky said, that she can't support that kind of an effort and that it would hurt her campaign, which would put more pressure on Obama to stick to the U.S.'s traditional backing of Israel at the U.N.

In her letters, addressed to Hoenlein, major donor Haim Saban, Gerrald Silverman, president of the Jewish Federations of North America, and several others, Clinton said she looked forward to working together to oppose the boycott movement.

"I know you agree that we need to make countering BDS a priority," Clinton wrote. "I am seeking your advice on how we can work together ... to reverse this trend ... and fight back against further attempts to isolate and delegitimize Israel."