US President Donald Trump has ridiculed Beto O'Rourke just hours after the Democratic presidential hopeful ended his campaign.
The president used a profanity to describe his rival and said he "quit like a dog".
O'Rourke, a former Texas congressman, was highly critical of Trump after a mass shooting in his hometown of El Paso in August.
He called the bloodshed a "consequence" of Trump's anti-immigrant rhetoric.
On Friday Mr O'Rourke said he was quitting the race for the White House as his campaign did not have "the means to move forward successfully".
Trump's response came days after he said Islamic State (IS) leader Abu Bakr al-Baghdadi had "died like a dog" during a US military operation in north-western Syria.
Speaking at a rally in Tupelo, Mississippi, the president branded O'Rourke a "poor, pathetic guy".
