Dermer worked as a political consultant for Natan Sharansky in the 1999 campaign, and from January 2001 for nearly three years he wrote a column "The Numbers Game" for "The Jerusalem Post". In 2004, he and Sharansky co-wrote the best-selling book "The Case For Democracy: The Power of Freedom to Overcome Tyranny and Terror", famously endorsed by then US-President George W. Bush. In 2005, while Benjamin Netanyahu served as Finance Minister under Ariel Sharon, Dermer was appointed economic envoy at the Israeli embassy in Washington, a post for which he had to give up his American citizenship. In 2008, after his return to Israel, he became adviser to Netanyahu, who became Israel's prime minister in April 2009. Dermer is considered Netanyahu's closest adviser and strategic consultant. According to "The Jerusalem Post", he "runs much of the interference with the White House, and is intimately involved in the diplomatic process with the Palestinians, [... and] writes many of Netanyahu’s speeches".