If Donald Trump can continue his recent stretch of staying on message, he should be able to defeat Democrat Hillary Clinton, Rick Santorum told CNBC on Thursday.
"The winds are behind him. This is a race that Donald Trump should win," said Santorum, who had been among the many hopefuls for the GOP nomination won by Trump.
"What Donald Trump needs to do, and I think he's proved it over last couple of weeks, [is] that he can be disciplined [and] someone we can trust to be able to execute on the things he says he wants to do," Santorum said on "Squawk Box."
In his trip to Mexico, Trump showed he can conduct himself in a presidential manner on the world stage, Santorum said. "I think he handled himself exceptionally well."
Trump's subsequent Arizona speech on immigration grabbed the "middle ground," the former U.S. senator from Pennsylvania said.
Santorum argued the billionaire real estate mogul was able to strike a balance between calls for tough border security and a priority to deport undocumented immigrants who are criminals. "We're going to focus on certain people. We're not going to focus on others."
Ex-US ambassador to Mexico less sanguine
Antonio Garza, former U.S. ambassador to Mexico, was less sanguine about Trump's immigration overtures. In a separate "Squawk Box" interview, he said it's time to tackle border security.
"It's not that people [in Mexico] are oblivious to the challenges. But it's necessary they be talked about calmly, cool-headed, and with a real focus on getting things done, not simply scapegoating one country or the other," said Garza, who was appointed as ambassador in 2002 by then-President George W. Bush.
"But when the discussions are on building walls … and less on objectives of safe, secure, and efficient borders and the tone is more about closing the borders and deporting 11 million people, which is impractical, then I think you've moved away from the ability to have a calm, level-headed discussion about immigration reform to simply demagoguery," he added.
Trump's chances in swing state Pennsylvania
Back on the campaign trail, in the swing state of Pennsylvania, Santorum predicted Trump will pull people out to the polls who don't normally vote. "At least in my state, he has some attraction to Democrats and independents."
The latest RealClearPolitics polling average shows Clinton with a 7.3 percent lead in Pennsylvania in a two-way race with Trump and a 3.6 percent advantage over Trump nationally in a four-way race with the two third-party candidates.
Overall, Trump should continue to get more and more support among establishment Republicans, Santorum said. "It would be great if he got the same percentage as Mitt Romney did among Republicans, yes. I think he can get there, I actually do."
Santorum unsuccessfully ran for the Republican presidential nomination this year and in 2012, when it went to Romney who ultimately failed to prevent President Barack Obama from serving a second term.