Did you watch the NewsHour with Gwen Ifil tonight 12/17?

If you did could you explain to me Harlan Watson's(senoir U.S. climate negotiator) response to Gwen's question why the U.S. would not set specific emission cuts? He only said something like he didn't want to predetermine outcomes, very brief answer and I didn't understand what he meant by that at all. Please explain it to me if you caught that and know what he was saying.