Chuck Hagel, President Barack Obama’s nomination for US Secretary of Defence must wait before he is confirmed in the post.
Senate Republicans blocked narrowly a confirmation vote a tactic known as filibustering. President Obama said it was “unprecedented”.
The vote was just two short of the majority needed.
It’s expected the former Republican senator will win full Senate approval for the role in a vote later this month.
Some politicians have complained Hagal has been too critical of Israel and soft on Iran following reported comments.
Republicans have also sought more specific information from President Obama about the deadly September 11 attack on the US consulate in Benghazi in Libya.
White House spokesman John Earnest said a Republican is being blocked by Republicans and that does not send “a favourable signal” to the world.