He wished Philip was in Washington.

He knew Laura, and she had a great respect for his character, his opinions, his judgment.
Perhaps he, as an uninterested person whom she would have some confidence, and as one of the public, could say some thing to her that would show her where she stood.
Philip saw the situation clearly enough.

Of Laura he knew not much, except that she was a woman of uncommon fascination, and he thought from what he had seen of her in Hawkeye, her conduct towards him and towards Harry, of not too much principle.

Of course he knew nothing of her history; he knew nothing seriously against her, and if Harry was desperately enamored of her, why should he not win her if he could.
If, however, she had already become what Harry uneasily felt she might become, was it not his duty to go to the rescue of his friend and try to save him from any rash act on account of a woman that might prove to be entirely unworthy of him; for trifler and visionary as he was, Harry deserved a better fate than this.
Philip determined to go to Washington and see for himself.

He had other reasons also.