WASHINGTON – President Obama will play diplomat this coming week during a global trip, with emphasis on one special relationship and an increasingly awkward one.

The trip will provide a reminder that the UK remains America's closest ally and will highlight Germany's standing as a European power. But it will also provide the latest illustration of how another longtime ally, Saudi Arabia, continues to drift from Washington's orbit.

On such issues as the fight against ISIL and dealing with Iran, there are many strains to the U.S.-Saudi relationship. White House officials have been critical of Saudi leaders and the heads of other Sunni Muslim countries, urging them to do more to confront the terrorist group

The Gulf Cooperation Council summit will include Saudi Arabia and the Persian Gulf states of Bahrain, Kuwait, Oman, Qatar and the United Arab Emirates.

Sen. Tim Kaine, D-Va., a member of the House Foreign Relations and Armed Services committees, said U.S. officials "want them to be all in on ISIS" but instead "we don't see an urgency on their part."

The frustration cuts both ways. Saudi officials and their Sunni allies wonder why Obama has taken a more hands-off approach than many of his predecessors.

Obama heads to Saudi Arabia for a meeting Wednesday with the Saudi leader, King Salman bin Abdulaziz Al Saud. Obama, Salman and the other GCC leaders will then hold three distinct sessions. There will be one on ISIL and Al-Qaida, and another on general regional stability.

But there also will be one on a more touchy issue for the Sunnis: "Iran and regional security and our efforts to prevent destabilizing actions across the region," said Ben Rhodes, deputy White House national security adviser.

There will be disagreements and calls to strengthen joint efforts. But many lawmakers agree that Obama will hear one strong message from Sunni leaders about fighting ISIL. "They're looking for the U.S. to lead an effort and they'll join in," said Senate Foreign Relations Committee Chairman Bob Corker, R-Tenn.

Arms sales have long been a part of U.S. dealings with the Saudis and other Sunni nations. To that end, Corker said many lawmakers want Obama to announce that he is green-lighting deals with Qatar and Kuwait.