In less than a year in office, Trump has led the G.O.P. into situations and alliances so degraded that the Party may never fully recover, even as he watches an investigation into Russia’s possible interference in the 2016 election, led by Special Counsel Robert Mueller, move ever closer to his immediate circle. Last week, Donald Trump, Jr., refused to answer questions before the House Intelligence Committee about his conversations with his father, and a plea deal that Mueller struck with Michael Flynn, the former national-security adviser, indicates that Trump’s son-in-law, Jared Kushner, may be under scrutiny, too. Mueller may also have turned his attention to records related to Trump’s finances.