Imagine hosting a large gathering of supremely important people. Protocol is taken seriously.

But there are at least two complications with the arrangements: One longtime leader has lost interest in the meetings but cannot be shunned outright. Another guest is increasingly influential but has a barely official invitation to the party in the first place.

Whom to seat at the head table and whom to stash in the back by the kitchen?

This is the diplomatic quandary facing hosts of the U.N. climate change conference that begins today in Bonn, Germany. The U.S. government—the longtime leader of the climate battle, but whose interest has dwindled under the Trump administration—has sent a delegation to join international leaders as they hash out further terms of the 2015 Paris climate agreement. Stepping into the breach is the increasingly influential Gov. Jerry Brown, who will preside over a series of events on the periphery of the conference.

Absent a seat at the negotiating table, Brown has a role organizing state and local officials from around the world who are increasingly seeking to craft their own climate deals, independent of what their nations’ leaders do.

A State Department official said Under Secretary of State for Political Affairs Thomas A. Shannon, Jr., will head the U.S. delegation, but the agency has not officially released further information.  The federal contingent might well be expected to take the lead at such a conference. But that leadership has been complicated by the Trump administration’s announced intention to pull out of the Paris agreement, lumping the U.S. with Syria as the world’s only nations to reject the deal. Thus it is difficult to determine the extent of the influence the United States will have in Bonn to continue shaping an accord it has publicly repudiated.

Brown, on the other hand, is rallying a powerhouse group of international officials who are creating their own carbon-trading markets and entering into agreements pledging to reduce greenhouse-gas emissions. In recognition of his leadership of these “sub-nationals,” Brown has been named the conference’s Special Advisor for States and Regions.

Do the circumstances make California the de facto U.S. leader at the conference?

No one state is taking the lead, but “California is definitely a leader,” said Washington Gov. Jay Inslee, a participant who along with Brown and New York Gov. Andrew Cuomo—all Democrats—created the U.S. Climate Alliance, a group of states that coordinate their climate policies. “California has always led the country in so many respects, and many of the policies implemented at the state level can be replicated in other states, nationally and internationally.”

In an interview on the eve of the trip, Brown struck an urgent tone about the threat of a warming world and welcomed the Trump administration to join his “crusade.”

“We’d be glad to work with the federal government,” Brown said, while making clear that California would be comfortable going its own way. “We’ll coordinate to the max with the U.S. government and anyone else who will join in this crusade. It’s going to be a Herculean effort, never undertaken by a state government before.

“But given the absence of leadership in Washington,” Brown continued, “the mantle of leadership falls on California, and we won’t shirk it.”

Brown and California Senate leader Kevin de Léon, a candidate for U.S. Senate, began their trips by speaking on climate change at a Vatican symposium. Next the governor embarks on a whirlwind series of events at the European Parliament and meetings with officials in Belgium, Germany and Norway before settling in at Bonn for the climate conference, which runs from Nov. 6-17. De Léon and other California officials will also attend.

It is unclear how seriously the Trump administration is taking the Bonn conference, which is officially called the 23rd meeting of the Conference of the Parties to the U.N. Framework Convention on Climate Change. Also known as COP23. The conference will focus on negotiations to establish rules on how each of the signatory nations’ voluntary goals for lowering greenhouse-gas emissions should be accomplished and verified.

Although President Trump has spoken of reworking the pact, it is non-negotiable. In addition, the U.S. is bound by the Paris framework at least until 2020. That leaves the U.S. representatives in a potentially uncomfortable position.

While the official climate conference takes place in a large plenary hall and in meeting rooms, dozens of parallel events will be held in a setting that resembles a sprawling world’s fair: huge tents with exhibits and pavilions hosted by countries and non-governmental organizations.

Deals and agreements may emerge from these venues, and that’s where Brown and the California contingent will operate. The state’s role as disrupter could be tempered by its pitch to global industries and investors that California’s strict carbon-cutting policies are compatible with a robust and expanding economy.

“We’ve taken these environmental challenges and we have turned them into incredible economic opportunities,” de Léon said. “Through our policies, we are sending a very clear market signal that attracts the necessary capital that is critical to create the technologies that are vital to reduce our greenhouse gases. And the biggest venture capitalist of them all is the state of California. We are the angel investors, sending the right market signals.”

Matt Rodriguez, head of California’s Environmental Protection Agency and a veteran of world climate meetings who is heading to Bonn, said that it’s results, not titles, that get the attention of international officials.

“I remember traveling in China in 2013 and happened upon a gentleman who worked at the English consulate in Shanghai,” Rodriguez said, recalling a trade mission during which California officials were also discussing renewable energy and climate change. “I told him I was having difficulty finding the right people to talk to, wondering if we were approaching this correctly.

“He said, ‘It really doesn’t matter; the rest of the world is interested in what California is doing right now. They know you have an aggressive program to reduce carbon, and you are achieving results and it’s not harming your economy.’ That’s all that mattered.

“I remember that when I get a little bit tired,” Rodriguez said. “I don’t know that there are many states that have this kind of influence.”