I think the court is going to make its ruling based on the language of the 1977 statute in which the President can impose tariffs without approval of Congress in the event of a "national emergency."

Since "national emergency" is rather undefined, and apparently the statute in question gives the President the discretion to declare one, and further Congress has not spoken in opposition to Trump's tariff--and also, the Trump opponent's lawyer admitted that Trump has the power to do what he's doing no matter what, even if not under this particular statute, through other means;

I don't think that's the focus of the case.

Almost all of the briefing and oral argument wasn't focused on "national emergency"; it was focused on "regulate." Neither the Justices nor any of the counsel really want to dig into whether (or how) the courts could parse whether a President had correctly identified a "national emergency." Instead, nearly the entire argument turns around the scope of what power the President is allowed to exercise after a national emergency has been identified. Specifically, whether the IEEPA's grant of authority to the President to "regulate" international trade in the event of an emergency includes the power to impose tariffs on international trade.

From the oral arguments, the Justices appear to be divided 3-3-3 on the issue. Thomas, Alito, Kavanaugh seem convinced that the Administration is correct; Jackson, Kagan and Sotomayor seem convinced they're wrong. ACB, Roberts, and Gorsuch all were more in the middle, with both ACB and Roberts having real problems with how the Administration's position can be squared with their Major Questions Doctrine cases, and Gorsuch seeming to delight in the possibility of resuscitating the Non-Delegation Doctrine in a major case.