LAT:

Election lawyers say the pledge is not legally binding because it does not promise the parties anything in return for their loyalty.

“As a matter of contract law, it doesn’t look like an enforceable contract,” said UC Irvine law professor Richard Hasen, who specializes in election law.

“To be a binding contract, they have to be giving something, and what could they give?” Hasen asked.

Trump told reporters he received “absolutely nothing, other than the assurance that I would be treated fairly” in return for his signature, a statement that might leave some room for later interpretation. Asked whether he would change his mind, he said, “No, I have no intention of changing my mind.”

The party appears to be simply banking on candidates’ unwillingness to break a promise, Hasen noted.

“If [Trump] later changed his mind, he would be painted as a hypocrite for promising one thing and doing something else,” Hasen said.

Michael Kang, a professor at Emory University in Atlanta who has written about election laws, called the pledge “an attempt to replicate the effect” of so-called sore-loser laws. Such laws stipulate that a registered primary candidate cannot switch parties or become an independent to run in a general election, though states rarely apply them to presidential candidates, Kang and Hasen said.

Kang called the enforcement of such a pledge an “open question.”

“It’s safe to say that there would be constitutional questions about their enforceability,” Kang said.