On Saturday, leaving the White House for a trip here for a Republican fund-raiser and a speech on Israeli-American relations, Mr. Trump told reporters that “they are devastated in Saudi Arabia,” noting that “the king will be involved in taking care of families and loved ones.” He never used the word “terrorism.”

What was missing was any assurance that the Saudis would aid in the investigation, help identify the suspect’s motives, or answer the many questions about the vetting process for a coveted slot at one of the country’s premier schools for training allied officers. Or, more broadly, why the United States continues to train members of the Saudi military even as that same military faces credible accusations of repeated human rights abuses in Yemen, including the dropping of munitions that maximize civilian casualties.

“The attack is a disaster for an already deeply strained relationship,” Bruce Riedel, a scholar at the Brookings Institution and a former C.I.A. officer who has dealt with generations of Saudi leaders, said on Saturday. It “focuses attention on Americans training Saudi Air Force officers who are engaged in numerous bombings of innocents in Yemen, which is the worst humanitarian catastrophe in the world,” he said, noting that the Trump administration had long been fighting Congress as it seeks to end American support for that war.

But even stranger, said Mr. Riedel, was “the president’s parroting of the Saudi line” before learning the results of an investigation into whether the gunman acted alone, or had allegiances to Al Qaeda or terrorist groups.