A member of the comitee recently expressed doubt that Israel has joined the 'thermonuclear club'. That is an interesting question in its own right, with a clear (yes or no) albeit sadly secret answer.
The official Israeli position is still to never confirm or deny their possession, which they call amimut, meaning opacity or ambiguity, and that Israel would not be the first country to introduce Nuclear Weapons to the Middle East. Israel is, despite all that opacity, generally presumed to have at least A-Bombs, fission weapons. It is known that they received French help in gaining nuclear capability. It was Mordechai Vanunu who made Israel's nuclear weapons program public. Certainly, Israel's security apparat has not forgiven Vanunu for fouling the nest (and converting to Christianity as if to add insult to injury from their PoV) and they will contuinue to silence him.
Wall of silence
Years back I had a peculiar exchange in a conversation with a Jewish Republican who scolded me for having referreded casually to Israel's nuclear weapons - these things should not be spoken of lest Israel's enemies learn of it! As if they needed me. While that admonition was hilariously absurd, it illustrates well the reality that politics have made US officialdom go to absurd lengths to not having to speak of the unspeakable - Israeli nuclear weapons:
"When the Senate Foreign Relations Committee published a 2008 report titled “Chain Reaction: Avoiding a Nuclear Arms Race in the Middle East,” it included chapters on Saudi Arabia, Egypt, and Turkey—but not Israel. The 61-page report relegated Israel’s nuclear arms to a footnote that suggested that Israel’s arsenal was a “perception.”
“This report does not take a position on the existence of Israeli nuclear weapons,” the report said. “Although Israel has not officially acknowledged it possesses nuclear weapons, a widespread consensus exists in the region and among experts in the United States that Israel possesses a number of nuclear weapons. For Israel’s neighbors, this perception is more important than reality.”
No there there? I beg to differ. It may be just me nitpicking, but I doubt even the wogs are so dumb they can be held at bay with rumours (irony alert), and that the Israelis, believers in hard power that they are, would want to rely on 'perception'.
The Symington amendment
US law (the Symington amendment of the 1961 Foreign Assistance Act) bars the US from giving aid to nations that engage in clandestine nuclear weapons proliferation. For many years, the US chose, under the influence of the pro-Israeli lobby, to ignore the law in how it was applied to Israel. The way to do so was to avoid, supress or dilute any public statement on Israel's nuclear weapons arsenal - and to punish offenders.
If Israel's nuclear arsenal was publicly acknowledged by the US, they would have to apply the Symington amendment and that would cut off all aid to Israel, and sever ties of technological cooperation. Because that must not be, Israel only 'appears to have nuclear weapons'.
A little circumspect, the CIA stated in the declassified Special National Intelligence Estimate 4-1-74 in 2008: “We believe that Israel already has produced and stockpiled a small number of fission weapons.” A little less circumspect, the DIA in 1999 asssessed Israel's current arsenal at 60-80 warheads (projecting it to 65-85 by 2020).
In the 2009 CSIS study "Study on a Possible Israeli Strike on Iran’s Nuclear Development Facilities" (pdf) Anthony Cordesman conservatively used the lower DIA numbers of 60-80 Israeli nuclear weapons. His section on Israeli nukes offers the following (and IMO most complete and non-circumspect publicly available) summary on p.9:
"Estimates of numbers and types of weapons differ sharply.♦ No agreement exists over the plutonium output from the reactor at Dimona. Which is reported at power outputs from 75-200 megawatts. Satellite photos indicate that output is more likely to be below 140 megawatts.
♦ Stockpile of at least 60-80 plutonium weapons.
♦ May have well over 100 nuclear weapons assemblies, with some weapons with yields over 100 kilotons.
♦ U.S. experts believe Israel has highly advanced implosion weapons. Known to have produced Lithium-6, allowing production of both tritium and lithium deuteride at Dimona. Facility no longer believed to be operating.
♦ Some weapons may be ER variants or have variable yields.
♦ Stockpile of up to 300-400 weapons is possible. Lower limit could be 70-100.
♦ There exists a possibility that Israel may have developed thermonuclear warheads."