Washington (CNN) Texas Sen. Ted Cruz's first shot at his expected Democratic challenger, Rep. Beto O'Rourke? Mocking his name.
As Tuesday's primaries were closing, Cruz's campaign released a 60-second radio ad that was a country music jingle prodding O'Rourke for going by "Beto" rather than "Robert."
"Liberal Robert wanted to fit in, so he changed his name to Beto and hid it with a grin," the song says.
O'Rourke said he's gone by "Beto" since he was born.
"My parents have called me Beto from day one, and it's just -- it's kind of a nickname for Robert in El Paso. It just stuck," he said in a brief phone interview Tuesday night.
O'Rourke has previously posted a baby picture of himself in a hand-stitched "Beto" sweater on Instagram.
He declined to comment on the Republican senator, whose given name is Rafael Edward Cruz, going by "Ted."
The Cruz radio ad also goes after O'Rourke for being liberal.
"If you're gonna run in Texas, you can't be a liberal man," the song says.
With O'Rourke leading the Democratic field as primary ballots are counted, the two could be headed for a faceoff in November. Texas has long been a Republican stronghold, but O'Rourke has outraised Cruz in recent months. After Hillary Clinton came within 9 percentage points of Donald Trump in 2016, some Democrats are hopeful that the state is poised for a major shift leftward.
CNN has rated the race as Likely Republican.
CORRECTION: This story has been updated to more accurately reflect the Cruz jingle's lyrics.