Rep. Mo Brooks’ new TV ad is titled “Build the Wall,” and he uses it to cast himself as a Trump ally and opponent of “establishment Republicans” who stand in his way, a sentiment that could determine who wins the Alabama Senate special election.

In the ad, Brooks says he will “fight every spending bill that doesn’t fund that wall,” if elected to the Senate, and he promises to “read the King James Bible” on the Senate floor to filibuster any such legislation.

Tying themselves to Trump, and especially his stance on immigration, could be the winning strategy for candidates in the Republican Senate primary in Alabama. In addition to Brooks, former Alabama Supreme Court Chief Justice Roy Moore and Sen. Luther Strange are running. The primary will be held August 15.

Trump’s endorsement could prove crucial in the deeply conservative state, the New York Times reported. Brooks could have a disadvantage in getting that because of his criticism of Trump while backing Sen. Ted Cruz in the Republican presidential primary. At the time he denounced Trump for “serial adultery.” Still, Strange is seen as the more establishment candidate, backed by Majority Leader Mitch McConnell, while Brooks may have more White House support.

Brooks is also receiving criticism from the conservative base for accepting an endorsement from anti-Trump group Courageous Conservatives PAC.

“I’m not going to engage in this kind of debate about whether an entity is 100 percent in agreement with me all the time,” he said in his defense. “They are conservatives who have the courage to stand up to establishment, moneyed candidates, and tried to get elected to various offices principled conservatives, and I agree with that.”

Gov. Robert Bentley appointed Strange to fill the seat vacated by Jeff Sessions when he left to become U.S. attorney general before Bentley resigned as he faced impeachment over a sex scandal. Brooks has said that Strange was appointed under “an ethical cloud.”

A recent Strange ad touted “Big Luther Supporting the Trump Agenda,” and opened with video of Trump saying, “We’re going to build a wall,” and leading a rally in chanting, “Build that wall!” Strange also voices his support for taking funding from “liberal sanctuary cities” in the ad.

Moore, for his part, is wearing his removal from the Alabama Supreme Court as a conservative badge of pride. He was removed as chief justice first in 2003 for disobeying a federal judge’s order to remove a Ten Commandments monument from the courthouse.

He became elected chief justice again in 2012 and suspended in 2016 for attempting to deny marriage licenses to gay couples after the U.S. Supreme Court decision allowing same-sex marriage. Southern Poverty Law Center President Richard Cohen, whose complaint led to Moore being removed, called him the “Ayatollah of Alabama” for his combining of religion and law.