There's still a chance for Ted Cruz to become the Republican presidential nominee, but he must defeat Donald Trump in Tuesday's primary in Indiana, a former U.S. congressman from the Hoosier State told CNBC.
"Donald Trump doesn't understand what the president does," David McIntosh told "Squawk Box."
"He's not the CEO of America. He runs the government. And the purpose of the government is to protect us, but let everybody be free to pursue their dreams."
While it's mathematically impossible for Cruz to win enough delegates in the remaining contests to clinch the nomination before the convention, a Cruz victory in Indiana could be the catalyst to put a contested convention back in play, said McIntosh, currently president of Club for Growth.
The free-enterprise advocacy group has been pouring millions of dollars into state contests to try to thwart Trump's drive to the nomination.
Following Trump's sweep of five state primaries last week, the RealClear Politics average of the latest polls puts the real estate mogul way ahead of Cruz in Indiana, 42.8 percent to 32 percent.
One poll last week had Cruz 16 points ahead of Trump.
On the national stage, Trump's support among Republicans and GOP-leaning voters is up 6 points to 56 percent, his highest yet in the NBC News|SurveyMonkey Weekly Election Tracking Poll.
Trump holds a 433-delegate lead over Cruz. Trump has 997. Cruz has 564.
According to NBC News, if Trump were to secure all of Indiana's 57 delegates, he'd need to win only 40 percent of the remaining delegates to reach the 1,237 needed to be the presumptive GOP nominee ahead of the July convention.