Updated at 5:50 p.m.: Revised to include a statement from Agriculture Commissioner Sid Miller.

AUSTIN — President Donald Trump on Tuesday urged his “many Texas friends” to vote in the Republican primary for Sen. Ted Cruz and other incumbents.

“I want to encourage all of my many Texas friends to vote in the primary for Governor Greg Abbott, Senator Ted Cruz, Lt. Gov. Dan Patrick, and Attorney General Ken Paxton," he tweeted. "They are helping me to Make America Great Again! Vote early or on March 6th.”

I want to encourage all of my many Texas friends to vote in the primary for Governor Greg Abbott, Senator Ted Cruz, Lt. Gov. Dan Patrick, and Attorney General Ken Paxton. They are helping me to Make America Great Again! Vote early or on March 6th. — Donald J. Trump (@realDonaldTrump) February 27, 2018

Five hours after his original tweet, which appeared to snub several other Texas Republican incumbents, Trump tweeted endorsements of Agriculture Commissioner Sid Miller and Land Commissioner George P. Bush, as well as Comptroller Glenn Hegar and Railroad Commissioner Christi Craddick. Miller and Bush are facing tough challenges in their primary races.

Texas LC George P. Bush backed me when it wasn’t the politically correct thing to do, and I back him now. Also, AC Sid Miller has been with me from the beginning, he is “Trump’s Man in Texas.” Also support Comptroller Glenn Hegar, and Railroad Commissioner Christi Craddick. — Donald J. Trump (@realDonaldTrump) February 27, 2018

Miller, who has boasted about having a close relationship with the president and served on Trump's agriculture advisory committee, runs political ads that label him "Trump's Man in Texas."

Miller said he was honored to receive Trump's endorsement Tuesday.

"Before President Trump was elected, I spent the majority of my time suing the Obama administration and its various agencies for their overreach and abuse of farmers, ranchers and landowners," he said in a prepared statement. "That stopped the day Donald Trump was elected. I look forward to continuing to work closely with him and his administration in the coming four years."

Ethics attorney Trey Blocker has launched a fierce campaign to position himself as further to the right than Miller and to discredit Miller's legitimacy as a conservative. He even landed a last-minute endorsement from a conservative group from East Texas called Grassroots America.

Brandon Rottinghaus, a political science professor at the University of Houston, said one way to measure the competition in a race is to look at endorsements.

“The ag race has been really interesting because there have been so many groups endorsing in different directions, it suggests there’s a split in the primary field,” Rottinghaus said. “They’re both getting support from different camps.”

“[Both Miller and Bush’s] races are going to be close because the incumbents are vulnerable,” he added.

Bush "swallowed a bitter pill" to endorse Trump in 2016 even after Trump disparaged Bush's father, former Florida Gov. Jeb Bush, and uncle, former President George W. Bush. He thanked Trump for his endorsement Tuesday.

"I am proud to accept President Trump's endorsement," Bush said in a news release. "I was proud to stand with him in 2016 and I am proud he is standing with me in 2018. I am also proud of the work we have done together to stop the Obama land grab and protect Texas private property rights."

Bush is also facing a tough challenge in his primary from former Land Commissioner Jerry Patterson.

He also scored the endorsement of another Trump: Earlier this month, Donald Trump Jr. tweeted his support for the incumbent and his disdain for Patterson.

"Elections are about choices," Trump tweeted. "In 2016, @GeorgePBush endorsed @realDonaldTrump and campaigned for him. His opponent attacked Trump and urged him quit the race. Texas conservatives have a clear choice: Bush for Texas Land Commissioner."

Elections are about choices. In 2016, @GeorgePBush endorsed @realDonaldTrump and campaigned for him. His opponent attacked Trump and urged him quit the race. Texas conservatives have a clear choice: Bush for Texas Land Commissioner. — Donald Trump Jr. (@DonaldJTrumpJr) February 6, 2018

The president's other endorsed incumbents are expected to win their primary races. Abbott met with Trump on Monday, along with governors of other states. He faces two little-known challengers in the Republican primary.

Cruz also appears poised to win, despite having four opponents. But the Democratic front-runner, U.S. Rep. Beto O'Rourke of El Paso, has been gaining attention and raised more money than Cruz in the first six weeks of 2018. Cruz tweeted his appreciation to Trump later Tuesday.

.@realDonaldTrump Thank you, Mr. President! Together, in 2017 we accomplished a lot for our country & we still have a lot of work to do: cutting taxes, reducing job-killing regulations, repealing Obamacare, and confirming constitutionalist judges who’ll defend the Constitution. https://t.co/MCJHCAi6uX — Ted Cruz (@tedcruz) February 27, 2018

Paxton has no primary challenger but still retweeted the president’s endorsement. Patrick is facing former Rockwall City Council member Scott Milder in the primary but has cash and name recognition as an advantage.

Texas kicks off the nation’s 2018 midterm elections with the first primary on March 6. Early voting continues through Friday.