There have been various "viral" versions claiming that Netanyahu endorsed X or Y circulating around the internet. They haven't been based on much. This is a good deal more substantial because it comes from Giuliani, who is a serious political figure, and Josh Rogin, who is a serious reporter and can't be accused of being a Trump supporter.
“I’ve talked to the members of the Israeli government at the highest levels. I know who they want elected here. It’s not Hillary Clinton. It’s not Obama 3,” Giuliani told me in an interview at the Republican National Convention in Cleveland.
In March, Giuliani traveled to Israel and met personally with Netanyahu, who has publicly remained neutral on the 2016 presidential election. Giuliani also met with several other senior Israeli government officials on his trip. According to him, Israeli government leaders fear that if Clinton were elected, she would pursue policies unwanted by the Netanyahu government, such as pushing to restart the Israeli-Palestinian peace process.
“They are politically aware enough to know that if Hillary gets elected, she is going to go further to her left, to protect her left flank against Elizabeth Warren,” Giuliani said.
“They know she’s going to start the two-state solution thing again, cave in to the Palestinians. They realize Donald Trump can say Islamic terrorism, can stand up to it. So there’s no question he would be better for the state of Israel than Hillary.”
One person close to Giuliani told me that during his March meeting with Netanyahu, the Israeli prime minister said he preferred Republican administrations to Democratic ones and gave Giuliani a message to personally deliver to Trump with suggestions about how Trump should talk about Israel-related policy issues. Giuliani met with Trump and his son-in-law, Jared Kushner, in New York following the trip and delivered the message, this person said.
Hillary's track record on Israel is really bad. Her relationship with Netanyahu is really terrible. She boasted that she was the designated yeller at him. She was to the left of her husband on Israel. Suffice it to say that it's no surprise that Netanyahu isn't looking forward to having to deal with Hillary Clinton for 4 to 8 years.
Giuliani is also carefully not to use Netanyahu's name, which gives this more credibility rather than less. Obviously Netanyahu's office is insisting that he has no position on the election. That is what you do in politics.