SAN ANTONIO – Eighteen candidates are running in the U.S. District 21 Republican primary election.

It's an open seat because longtime Rep. Lamar Smith decided to retire.

"We're a red state. Those who choose to run recognize that and have the wind at their backs. So they have a very good chance of remaining in that seat for a very long time whoever wins," said Sharon Navarro, UTSA associate professor of political science and Geography.

Navarro said the GOP primary race for the 21st Congressional District speaks to the changing nature of politics across the board.

Eighteen candidates are vying for the Republican nomination, including state Rep. Jason Isaac.

Chip Roy has received the backing of his former boss, Sen. Ted Cruz, and Jenifer Sarver, a former aide to U.S. Sen. Kay Bailey Hutchinson.

"They realize that this is an open seat, so it's anyone's to win. The donors haven't been pre-selected, so it's anyone's chance at grabbing a donor," Navarro said.

Along with the number of names on the ballot for this particular race, experts say something else that makes it interesting are the candidates themselves.

Since the late '80s, Smith has consistently held this seat. More than 800,000 people live in the district. It stretches nearly 6,000 square miles, from north San Antonio, up Interstate 35 and into Austin. 

These candidates are reflecting the diversity of the region.

"They look entirely different than from Lamar Smith. Age-wise they're different - descriptively, they look different. You have women, you have a minority running in that race," Navarro said.

And with such a crowded field, Navarro said name recognition is important.

Social media helps give candidates an accessible platform to spread their message.

"When we have an open seat it tends to be the norm. In this case we're still red and people are trying to ride that coat-tail," Navarro said.

The following is list of the District 21 candidates: