Trump has repeatedly criticized USA intelligence agencies for allegedly being biased against him in their investigations into Russian meddling in the 2016 United States election. "Maybe we'll give that a shot some day", Trump continued, prompting laughter from the audience.
Trump and Xi met on multiple occasions during Trump's first year in office, including a trip Trump made to China and a weekend Xi and his wife spent at Mar-a-Lago in April.
Mr Trump attacked Mr Sessions for asking the inspector general to investigate potential surveillance abuses by the FBI in the early stages of the Russian Federation investigation, saying that such a probe should be handled instead by "Justice Department lawyers".
"And look, he was able to do that".
"I think it's great", Trump added.
The official Xinhua news agency reported last Sunday that the party's Central Committee has proposed removing from the constitution a stipulation stating that the president and vice-president "shall serve no more than two consecutive terms".
China has been the main target of Trump's anger over the USA trade deficit since his presidential campaign, but its steel and aluminum exports to the United States are minimal.
Xi, 64, was elected again as the party chief in October 2017, allowing him a second five-year term.
Trump ratcheted up the rhetoric on Saturday, threatening a tax on cars from the European Union if it takes retaliatory measures.
Even as a joke, the comments seemed to make light of what has been seen as Xi's consolidation of power in China.
There have been widespread concerns among Chinese activists and critics of the government that world nations have not rallied against Xi's step enough.
Earlier, White House said that it was up to China to set presidential terms.
He also slammed former Republican President George W Bush and US intelligence agencies for the decision to invade Iraq in 2003, after incorrect intelligence indicated it had weapons of mass destruction.