Lieberman does not control the IDF, which Barak does, nor even the Shin Bet or Mossad which answer to Netanyahu. Thus, Lieberman cannot issue threats on his own. It is true that Lieberman has influence in the government, but his influence is mostly in the area of what steps should NOT be taken rather than on what steps should be taken (since everybody knows his ideas are just too brute). So as Lieberman's teacher, Stalin said: no divisions, no power to his threats.
Key U.S. House Democrat cites troublesome issues in Iran nuclear deal (Reuters)
from the article: Lieberman: If Gaza rocket fire does not stop, there will be consequences