"At the end of the day, we truly believe that Ted Cruz is the most consistent and principled conservative who has the ability to not only win Iowa but I believe to win the [Republican] nomination," he told the paper.
He also addressed why he didn't support any of the other candidates polling towards the top in Iowa — Trump, Ben Carson, or Sen. Marco Rubio (Fla.).
While speaking generally about Trump and Carson, Vander Plaats reserved his harshest critique for Rubio, the candidate seen as Cruz's biggest threat outside of Trump. Vander Plaats blasted Rubio's support for a bipartisan immigration reform bill.
"The one issue he decided he was going to lead in Washington, D.C., with [Sen. Charles] Schumer (D-N.Y.) and [Sen.] John McCain (R-Ariz.) and the 'gang of eight' gave and gives everybody a little bit of cause for pause," he said.
"And with immigration being such a big issue today, I think that's going to be a hurdle that's going to be a very steep for Marco Rubio to clear."
Vander Plaats's endorsement could help Cruz.
Santorum had polled regularly in the single digits before Vander Plaats endorsed him in December 2011, according to RealClearPolitics. But the former senator gained strength from that point and ended up winning the caucuses.
Cruz has long worked to bring key evangelical leaders in the state onto his side. Evangelicals made up almost 60 percent of the GOP caucus vote in 2012.
Cruz is also being supported by Rep. Steve King (R-Iowa) and radio host Steve Deace, two other key figures within the state's evangelical community.