The Mueller investigation into tRump has stretched on for months, and is apparently becoming a multi-headed beast, including the original topic of collusion with the Russians, along with obstruction of justice and money laundering. When tRump decided that he didn't like the idea of being investigated by people (Comey) under his direction, in a very Nixonian move - he fired them. That's when hell really broke loose.
With the appointment of Mueller, things got murky for the Republicans. They started their own congressional investigations and pretended to care. But once the indictments started dropping, and Papadopoulos made a deal, they knew they had to do something.