http://www.fas.org/nuke/guide/pakistan/nuke/chron.htm
1985--U.S. Nuclear Export Control Violation: Texas, krytrons (nuclear weapon triggers).
1985--U.S. Nuclear Export Control Violation: US cancelled license for export of flash x-ray camera to Pakistan (nuclear weapon diagnostic uses) because of proliferation concerns.
1985/6--Media cites production of highly enriched, bomb-grade uranium in violation of a commitment to the US.
1986--Bob Woodward article in Washington Post cites alleged DIA report saying Pakistan `detonated a high explosive test device between Sept. 18 and Sept. 21 as part of its continuing efforts to build an implosion-type nuclear weapon;' says Pakistan has produced uranium enriched to a 93.5% level.
1987--U.S. Nuclear Export Control Violation: Pennsylvania, maraging steel & beryllium (used in centrifuge manufacture and bomb components).
1987--U.S. Nuclear Export Control Violation: California, oscilloscopes, computer equipment (useful in nuclear weapon R&D).
1989--Multiple reports of Pakistan modifying US-supplied F-16 aircraft for nuclear delivery purposes; wind tunnel tests cited in document reportedly from West German intelligence service.
1989--Test launch of Hatf-2 missile: Payload (500 kilograms) and range (300 kilometers) meets `nuclear-capable' standard under Missile Technology Control Regime.
1990--US News cites `western intelligence sources' claiming Pakistan recently `cold-tested' a nuclear device and is now building a plutonium production reactor; article says Pakistan is engaged in nuclear cooperation with Iran.
I think Pakistan had viable weapons prior to Clinton being in office. Really, if you look at the time-line provided on the link, Clinton's administration did more to prevent Pakistan for fielding nuclear weapons than either of the previous two administrations.
By the way, those are US Nuclear Export Violation that occurred under Reagan and Bush. No violations under Clinton. Just a bomb going off that was built and researched under the previous administrations.