Iran's messianic death wish came to power on August 15th 2005 and it took time for Ahmadi-Nejad to place his IRGC Commanders into key posts and get himself and lunatic Ayatollah Mesbah Yazdi positioned to remove Supreme Ruler Khamenei or former president Rafsanjani should they oppose the neo-Iran regime.
Rafsanjani's son was arrested in a show of power (later released when Rafsanjani backed down) and Khamenei believes his liver cancer comes from being poisoned.
As their readiness increased so did the threats. The old nuclear weapons Iran had acquired (around a dozen units) were not missile capable and nore of the dirty bomb use kind. What they are trying to develop is small powerful weapons they can put into their almost ready long range missile.
There are several simultaneous matters in play so simply eradicating Israel is only a showpiece not a true end all and be all for now. Not until other aims have been achieved by the neo-regime.
Destruction of Israel priority will change if Iran is attacked militarily.