Binyamin Netanyahu and Avigdor Lieberman have a lot in common.
Both are shrewd and cynical political operators who, despite all they have done, are still treated by the old Israeli elite as outsiders. Both are regarded by the international media as dangerous hardliners. Neither let any of that stand in their way in their struggle to reach the top. And both made millions in the short breaks they took from their meteoric political careers.
Little wonder that Mr Lieberman, as a young Likud activist, was one of the earliest supporters of Mr Netanyahu when he first ran for the Knesset in 1988. For the next decade, the two were inseparable. Mr Lieberman was working behind the scenes for his political master and, when Mr Netanyahu became Likud chairman in 1992, he appointed him as party manager.
In 1996, when Mr Netanyahu became prime minister against all odds, he made Mr Lieberman director general of his office. But that was when their relationship began to strain.
Mr Lieberman expected Mr Netanyahu to adopt a more forceful manner of governing, to take on all parts of the establishment that did not want to accept his premiership - to essentially lead a presidential-style administration. Instead, he felt that Bibi was too willing to please and not decisive. After a tumultuous first year in office, he resigned and left Mr Netanyahu on his own for the rest of his term.
Mr Lieberman went into business brokering deals between Israeli companies and the former republics of the Soviet Union. Some of these deals are now part of the ongoing investigation into serious allegations of money-laundering. But he did not stay out of politics for long, and a year later was already laying the groundwork for his new party, Yisrael Beiteinu.
Most observers assumed that the party was simply a "satellite" of Likud, aimed at bringing the new Russian immigrants into a Netanyahu-led coalition. But it gradually emerged that Mr Lieberman was acting on his own long-term agenda. His party's ideology was not different in any significant way to that of Likud, but the manifesto was not the main point. Yisrael Beiteinu was founded as the platform that would propel Mr Lieberman to the leadership of the right wing and from there to the Prime Minister's Office.
He served in the governments of Mr Netanyahu's rivals, Ariel Sharon and Ehud Olmert. In 2006, when Likud under Mr Netanyahu received only 12 Knesset seats, Yisrael Beiteinu almost overtook them at the polls.
Mr Netanyahu's return to the premiership last year has not changed the Lieberman strategy. He has patience.
That is the underlying reason for all the tensions between the two. The former assistant is convinced that he can do a better job than his old boss.