Vice President Mike Pence is joining President Trump in endorsing Luther Strange in the Alabama Senate special election primary, as people headed to the polls on Tuesday.

"Luther Strange has stood shoulder-to-shoulder with President @realDonaldTrump and is supporting our agenda to #MAGA," he said in a tweet.

Trump endorsed Strange last week, and reiterated that support on Monday, mentioning that Strange is "strong on Border & Wall, the military, tax cuts & law enforcement."

Strange has been serving as senator since Jeff Sessions became Trump's attorney general in February.

Also in the running for the GOP nomination is Rep. Mo Brooks, a member of the conservative Freedom Caucus, and former chief justice of the Alabama Supreme Court Roy Moore.

The top two winners will advance to a runoff if no one is able to get 50 percent of the vote. The special election is on Dec. 12.