President Donald Trump has a lot on his agenda for this week’s sitdowns with China’s Xi Jinping, but pushing his counterpart to show mercy to Jimmy Lai would serve them both well.

Lai, 78 and in poor health, will die in prison all too soon if not allowed to join his children in exile — a martyrdom that will be a permanent irritant in Beijing’s relations with the West and a constant reminder that Hong Kong no longer has true rule of law and China’s rulers don’t keep their word.

Trump has gotten hundreds of political prisoners released, testament to both his negotiating skills and his deep regard for individual suffering; winning the release of Lai would be his biggest triumph yet.

A kangaroo court in Hong Kong this year sentenced Lai to 20 years (after he’d already been jailed for six) on trumped-up charges; his real “crime” was to fight for the liberties that Beijing had vowed to preserve when it regained control of the island city in 1997.

Notably, his sentencing included hundreds of references to Team Trump: China’s authorities have already made this personal for the president.

Trump has pushed Xi on freeing Lai before, but now the Chinese premier will be in the president’s own home, where the appeal carries maximum human leverage.

No one will see Xi as weak for making this concession: The record of his rule is crystal-clear.

By contrast, refusing signals that he wants the world to know him as utterly heartless and determined to crush all critics — a man who can’t actually be trusted to honor any civilized code.

China’s power is such that others will still try to negotiate with Xi, but getting to any deal will be that much harder — and Beijing in fact has goals that only diplomacy can achieve.

The issues on the Trump-Xi table span the globe, from the Ukraine and Iran wars to AI, rare earths and a long list of trade concerns; inching forward on any of them will challenge both leaders.

But small steps can lead to far larger gains, and Jimmy Lai’s fate is by far the easiest question to settle.

Trump should push Xi on Lai to better know what kind of man he’s dealing with, and Xi should at long last give in because it’ll help him do what’s best for China.