40% of voters support Trump. That 40% comes from the half of the country that votes Republican in any given election.
But if we were to form a new White Party, the party of White Grievance/White Supremacy, then the Republican Party would be gutted, and have just 10% of the national vote.
If the Republican Party condemned Trump for, you know, attempting a coup, Trump would leave the Republican Party and take his idiot voters with him and start a new party - the White Party.