For one, general election polls this far out in the race are notoriously unreliable. But also, Trump doesn’t lead Clinton in many polls. In fact, he trails her in almost every recent poll as of early March.
Immigration is down
He’s trailing her
This is a really popular oversimplification in the modern Republican party. What’s never mentioned by Cruz or fellow conservatives is that the Carter administration had already negotiated with Iran for the release of the 52 American hostages long before Ronald Reagan was president. Jimmy Carter leveraged $11-12 billion in frozen Iranian assets in arranging for the hostages’ release. This was chronicled in detail by Politifact when Marco Rubio told the same story (he was given a “Pants on Fire” rating).