WASHINGTON -- The U.S.'s relationship with Saudi Arabia has weathered disagreements over how to rein in Iran, regime change across the Middle East and several large military adventures. Now it faces a new question, which was crystallized Friday in a speech by influential progressive Sen. Chris Murphy (D-Conn.)

"No one has a particularly credible long term strategy [for the Middle East] because it would involve facing some very uncomfortable truths -- about the nature of the fight ahead of us, and imperfections of one of our most important allies in the Middle East, Murphy said in a speech at the Council on Foreign Relations in New York.

The carefully worded address pointed to Saudi Arabia's backing of extremist Islamic ideology and its reckless military intervention in Yemen as evidence of the need to question unwavering U.S. support for the kingdom.

"For all the positive aspects of our alliance with Saudi Arabia, there is another side to Saudi Arabia" that America doesn't often see, Murphy said. "And it is a side that we can no longer afford to ignore as our fight against Islamic extremism becomes more focused and more complicated."

Murphy's frank and measured critique is one of the most high-profile of its kind, evidence in itself that questioning the relationship between Washington and Riyadh is becoming less of a political heresy.

Initially rooted in a shared interest in protecting the kingdoms vast oil reserves, the U.S.-Saudi partnership has evolved into a broad, shadowy military relationship that is difficult to fully detail.

The two countries cooperated to funnel fighters into Afghanistan to fight the Soviet Union in the 1980s, together kicked Iraqs Saddam Hussein out of Kuwait during the Gulf War, and have now grown closer in the broader war against groups like al Qaeda and the so-called Islamic State. The two are now supporting groups fighting in Iraq, Syria, Yemen and beyond.

Saudi Arabia has an outsized role in these efforts despite its relatively small population and weak military because it has bought more weapons from the U.S. than any other country in the world. Between 2009 and 2014, the U.S. delivered over $12 billion of weapons to the kingdom, much of which is being used in the bloody Saudi-led war in Yemen.