The soaring success of Donald Trump is causing considerable concern within Israel's corridors of power.

Although the Republican frontrunner has repeatedly promised that "Israel is safe" under him, his outsider status and lack of connection to the network of alliances and personal relationships that knit together Jerusalem, Washington and the American-Jewish establishment make a Trump presidency uncharted territory in every way.

The frosty relationship between Mr Netanyahu and President Barack Obama marked an all-time low in the strategic ties between Israel and the US, but the fields of disagreement were clearly identifiable.

Despite the fact that the two leaders clashed over the Iranian nuclear issue and, to a lesser extent, over the Israel-Palestine conflict, there were also improvements in security co-operation and intelligence-sharing. It is expected that despite lingering antipathy with Mrs Clinton, her presidency would continue to adhere to those ground-rules.

Even when the channels to the White House were obstructed, the Israeli government could always rely on the Republican Party, which controlled Congress, for support.

If Mr Trump secures the nomination and wins the general election, the general approach towards Israel in the White House or within the GOP will be much less predictable.

Mr Trump is not known to have ever expressed hostility towards Israel; on the contrary, he has taken part in various pro-Israel events, and his daughter, Ivanka, is a convert to Judaism. However, the fact that he told Jewish Republican donors "I don't want your money", that he has been endorsed by known antisemites such as David Duke and Louis Farrakhan, and that many of his voters back his anti-establishment image, all prompt concern over what his policies towards Israel might look like.

His recent promise to act as a "neutral" broker in the Israel-Palestine conflict - which he claims that only he can resolve - has done little to boost confidence.

For Prime Minister Benjamin Netanyahu, the choice between a Trump presidency and the Democratic frontrunner Hillary Clinton is even more dispiriting. When he was president, Mrs Clinton's husband, Bill, worked to end Mr Netanyahu's first term in 1999, and there is no sign that the Clintons feel any different towards him today.

Stung by past accusations that Israeli politicians have interfered in US elections, no senior figures are at this point speaking out in the open.

One result of the consternation over the next occupant of the White House is Mr Netanyahu's eagerness to sign the new 10-year defence agreement with the US before Mr Obama's term ends.

While the Israeli government does not officially support candidates in the American elections, Mr Netanyahu's preference in the 2012 race was clear from the warm reception he gave Republican nominee Mitt Romney in Jerusalem.