In what could have spiraled into a diplomatic nightmare, US sailors captured by Iran’s Revolutionary Guard on Tuesday were returned peacefully. While most are applauding diplomats on both sides, one US senator is stoking the fires, maintaining that the US Navy was within its full rights to enter Iranian waters.

On Tuesday, two small US Navy patrol boats lost contact with their command and drifted into Iranian waters in the Persian Gulf. Running aground on Farsi Island, the 10 crew members onboard the two boats were taken into custody by the Revolutionary Guard, and their boats were seized.

Many expressed concern that the incident could become a protracted diplomatic battle, but all crewmembers and equipment were released the following day after discussions between US Secretary of State John Kerry and his Iranian counterpart Mohammad Javad Zarif.

While the incident’s quick resolution is undeniably good news, US Senator John McCain, chairman of the Senate Armed Forces Committee, believes the American sailors should not have been taken into custody in the first place.

“The Administration is pretending as if nothing out of the ordinary has occurred. Vice President Joe Biden described the incident as ‘standard nautical practice.’ That assertion is patently false,” McCain said in a statement.

“What’s worse, by failing to affirm basic principles of international law, it places our Navy and Coast Guard vessels and the men and women who sail them at increased risk in the future.”

Democrats have argued that the swift return of the sailors was the direct result of the improved relations between Washington and Tehran after the summer nuclear deal negotiations. McCain refuted the claims.

“Furthermore, the suggestion by House Minority Leader Nancy Pelosi and others that the Iranian nuclear deal somehow aided in these sailors’ return is ludicrous,” he said, according to Breaking Defense, a military commentary website.

“These sailors were ‘arrested’ in apparent violation of international law and centuries of maritime custom and tradition.”

Republicans have insinuated that the Americans were mistreated while in Iranian custody, though video released by Tehran shows the sailors being treated to a full meal and comfortable accommodation.

“All indications suggest that our sailors were well taken care of, provided with blankets and food and assisted with their return to the fleet,” Secretary Kerry told reporters on Wednesday.

Circumstances surrounding how the Navy boats entered Iranian waters continue to unfold. US officials initially said a mechanical problem caused one of the vessels to drift toward Farsi Island, but that theory was proven false after the boats were driven back to Bahrain on Wednesday morning.

In an interview with Jorge Ramos on Thursday, US Defense Secretary Ashton Carter said the Pentagon now believes a navigational error was at fault.

“[The sailors] obviously had mis-navigated. That’s what they report. That’s how they believe they ended up in this circumstance,” he said.

After releasing the sailors, Iran’s Revolutionary Guard posted an online statement reading, “After determining that their entry into Iran’s territorial waters was not intentional and their apology, the detained American sailors were released in international waters.”