President Donald Trump's sweeping assertions of executive power during his first weeks back in office appear headed toward U.S. Supreme Court showdowns, but it remains an open question whether or how much the justices might act to check his authority.

While it was once rare for an administration to change its position in cases before the high court, Trump did so in his first term and has signaled he will do it again.

The Supreme Court also refused to pause briefing in a consolidated case involving appeals of two lower court decisions, Oklahoma v. EPA and PacifiCorp v. EPA. Both cases center on EPA’s denial of 21 state implementation plans for slashing ozone pollution that crossed state lines.