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.

An administration lawyer said a Tennessee law barring some medical treatments for transgender youths is constitutional and urged the justices to say so.