A decision made by the government in 1951 empowers "the foreign minister or someone appointed by him to sign international agreements and treaties on behalf of the government."
Two options were available to allow Netanyahu, who had already taken off for Washington, DC, to sign the deals: Either the government would need to meet to give him the power to do so or Ashkenazi, who was still in Israel, would need to give him the power to do so.
Once the issue was raised, the Justice Ministry spoke with the Foreign Ministry who spoke with Ashkenazi who signed to give Netanyahu the right to sign the agreement. Ashkenazi signed after he was informed that the deal would include a clause requiring the government to approve the deal before it takes effect, according to Channel 12.
Legal advisors to Netanyahu had believed that the prime minister was, in fact, authorized to sign international deals, while Ashkenazi is authorized to make decisions concerning internal matters.
A source in the Prime Minister's Office stated that at the last minute, when they had already landed in the US, they were informed that, according to Attorney-General Avichai Mandelblit, Netanyahu does not have the authority to sign the deal. Sources in the PMO criticized legal authorities for not warning them in time and claimed that Netanyahu is authorized to sign the deal and has done so in the past. Despite the criticisms, Netanyahu followed Mandelblit's decision on the matter.