WASHINGTON >> A coup leader with a penchant for song. A sultan with a taste for the high life. A ruthless prime minister with 31 years on the job. A former furniture salesman. A communist politburo veteran. A prime minister trying to shake off a $700 million financial scandal.

When President Barack Obama welcomes Southeast Asian leaders for a shirt-sleeves summit set to begin Monday in California, he’ll have some interesting dining companions.

U.S. officials say the unprecedented gathering, running through Tuesday, is the culmination of Obama’s seven-year effort to engage with the Asia-Pacific, a strategic push that China views as an attempt to contain its rise.

For the first time, the American president has invited to the United States all the leaders from the Association of Southeast Asian Nations (ASEAN), a diverse and democratically challenged 10-nation grouping. The meeting place is the sprawling Sunnylands estate where Obama hosted an ice-breaking summit with China’s President Xi Jinping in 2013.

During two days of discussions and a working dinner, the leaders plan to discuss economic cooperation and trade, and security issues.

ASEAN was founded in the 1960s as an anti-communist bloc. It now straddles all of Southeast Asia and has become a fulcrum of U.S. outreach in Asia. That includes its push for adherence to international law in the South China Sea, where disputes between China and its neighbors have stoked tensions.

But the U.S. faces an uphill battle to forge unity among ASEAN’s members, which includes poor nations such as Cambodia and Laos that are heavily influenced by China and are not party to the dispute. Others members such as Vietnam and the Philippines have been strongly critical of China after confrontations near contested islands.

James Clapper, the director of U.S. national intelligence, told Congress last week that ASEAN cohesion is challenged by “varying threat perceptions of China’s regional ambitions and assertiveness in the South China Sea.”

Another challenge for the U.S. lies in promoting a “rules-based order” in a region with a very mixed record on democracy and rule of law.

Several of the invitees have not come to power through free and fair elections.

They include Thai Prime Minister Prayuth Chan-ocha, who took power in a May 2014 coup, has cracked down on critics and dissidents and repeatedly pushed back the date for new elections. In the meantime, he has penned the lyrics to a tune called, “Returning Happiness to the People,” often played on state-controlled media.

Hun Sen from neighboring Cambodia is making his first official U.S. visit as leader, although he’s been prime minister since 1985. He has used a combination of guile and brute force to stay in power, including a violent coup in 1997. In recent months he has intensified pressure on the political opposition.

Daniel Russel, the top U.S. diplomat for East Asia, defended the invitations, saying the U.S. is not going overboard by rolling out the red carpet for “problematic leaders.” He said discussions at Sunnylands will be an opportunity to promote U.S. values and respect for human rights.

“Hun Sen isn’t going to hear it from his subordinates. Gen. Prayuth isn’t going to hear it from his colleagues, but they will and do hear from (Secretary of State) John Kerry, from Barack Obama,” Russel told reporters. “It’s important for there to be real communication here.”

Human Rights Watch, however, said inviting unelected leaders represents “an unearned diplomatic reward.” In a pre-summit report surveying the record of ASEAN members, it concluded most “have an extraordinarily poor human rights record.”

Among the 10 nations, only Indonesia and the Philippines are widely regarded as being open democracies. Vietnam and Laos have communist governments that prohibit political dissent, while tiny oil-rich Brunei is governed by the vastly wealthy Sultan Hassanal Bolkiah, one of the world’s few remaining hereditary leaders.

In 2014, Bolkiah introduced Shariah criminal law that calls for punishing adultery, abortions and same-sex relationships with flogging and stoning, an action that prompted a Hollywood boycott of the Beverly Hills Hotel, which he owns.

Also attending is Malaysian Prime Minister Najib Razak, who has been dogged by a scandal over a state investment fund and accusations of a lavish lifestyle. From neighboring Indonesia comes President Joko Widodo, a more down-at-heels leader who rose from being a furniture seller to running the world’s fourth-most populated country.

Four of the invitees are “lame ducks” with little time left in office, like Obama. At least one of them, from Myanmar, is skipping the summit and sending a deputy instead.

Still, Ernie Bower, a Southeast Asia expert at the Center for Strategic and International Studies, said the summit will demonstrate the importance of Southeast Asia to the U.S. and set a precedent the next president can follow.

“It will send a resounding message to Asian capitals that the United States is committed to this,” he said.