<<The dems pander to unions.
<<Unions are hot beds of racism.
<<You figure it out.>>
Easy. Your "hot beds of racism" is the key. The unions are no more "hotbeds of racism" than any other U.S. institution like the police, the army or the U.S. Senate. Your statement makes about as much sense as saying "the Democrats pander to the police and the police are hotbeds of racism."
An appeal to "the unions" will appeal to all union members, of which a certain percentage will match the percentage of racists in the general population. So a racist appeal to unions won't get all members, only the racists. The appeal to the unions has to be an across the board appeal to the common interests of all union members - working hours, pay, safety, etc. Yes the Democrats DO appeal to unions, on labour-rights issues.
OTOH, the Republicans appeal directly to racists (in code of course) but with an appeal based on racism, one that will draw in racists form unions, management, the religious etc.
When the Democrats appeal to unions, a certain number of union members interested happen to be racist and are drawn into the general appeal, which was not racist in essence. When the Republicans appeal to racists, they are looking for racists only and appeal directly (or as directly as they can) to their racism.