The President, in an act very Presidential, made sure to sit - forlornly - at a table showing that he was the bigger man. And by "bigger" he means that he should be allowed to bully anyone and get away with it.
It is important to note that neither Senator Schumer and Representative Pelosi shouldn't be needed in any case. The Republicans hold majority in both Houses of Congress and, with Princess Tiny Hands, the Presidency. The government shouldn't be at risk of shut down at all.
By the way, why would he want to create this dust up today. Is there something he wants to distract everyone from???