If they follow through they likely won't be successful in a presidential race but might be able to win some victories in all other areas.. But the Republican/Trump party might be screwed. Their narrow margin paths to victories will become even more difficult with the defection of even 5% of Republicans. But the Trump party is likely now more concerned about establishing obedience and loyalty in their base without a lot of thought to long term prospects.
We’d have a better legislative. More compromise. Coalitions. If they could siphon 30% from both parties.