"Presidents who have higher approval ratings generally have an easier time getting Congress to go with them on big ticket items (e.g., tax reform). That said, with the growing polarization within Congress, even a less popular president can get big stuff passed without being all that popular if his party holds the majority."
But even critics of President Trump have argued political pundits are focusing too much on Trump's unpopularity, and a president's approval ratings are not very important once he is in office.
"Trump didn't win the White House because people liked him. He won because a lot of Americans hated what their government had come to represent and trusted Trump to at least disrupt things. Trump's opposition will have no problem in 2018 and beyond demonstrating that things are broken. The trick will be selling the fix."