Trump knows that Nikki Haley poses no threat to his longterm goal of once again winning the nomination and the Presidency. Barring some drastic and unforeseen circumstances, I can’t picture a scenario where he does not walk away with the nomination.
But, I would imagine Trump would like to seal the deal sooner rather than later.
A convincing win in New Hampshire, though not mandatory, would absolutely go a long way for Donald Trump putting an end to this campaign once and for all. His opponents are hanging on by a thread, he knows this, and edging them out of the race once and for all means the sooner he can focus all his time and energy on Joe Biden.