evidence: Ron Klain, President Biden’s chief of staff, plans to step down in the coming weeks after playing a central role in steering the administration through its first two years, according to two people familiar with his plans, depriving the president of his top adviser as he enters a challenging new phase of his presidency. [...] Klain, 61, became the White House chief of staff after serving in the same role for Biden at the start of his vice presidency and holding other senior positions in the Barack Obama and Clinton administrations, including as chief of staff for Vice President Al Gore and Attorney General Janet Reno. Biden never seriously considered other candidates, and he used Klain’s selection to send an emphatic early message that Washington would be returning to a reliance on experience and order after the unorthodoxy and chaos of the Donald Trump years. In the Biden White House, Klain rose to become one of the most powerful chiefs of staff in decades, known for a fierce work ethic and for sending a constant stream of tweets, a habit that did not always endear him to fellow Democrats.