U.S. President Joe Biden’s envoys are pushing ahead with their effort to realign Middle East politics by brokering the establishment of diplomatic relations between Saudi Arabia and Israel despite significant concessions demanded by the Saudi monarchy.

Biden sent National Security Adviser Jake Sullivan back to Saudi Arabia in recent days, his second trip there in less than three months, as U.S. officials test the ground for an agreement bringing together two historic adversaries and fundamentally reshaping the region.

No breakthrough was announced, but the fact that Sullivan returned to the kingdom so soon after his last trip in May suggests that the Biden administration sees serious prospects for an accord. Among the hurdles has been Saudi Arabia’s insistence on a mutual security pact with the United States and development of a civilian nuclear program in which the country could enrich its own uranium, both nonstarters in the past.