For many people it isn’t a strongly motivating factor, whatever their opinion. The two parties are so far apart on this that if it’s one of your top issues you’ve already got your party. If you’re TOTALLY NOT “ok with millions of immigrants flooding into the country unabated, unvetted,” you’re already voting Republican so there’s no reason as a Democrat to pitch to you. Swing voters, on the other hand, don’t really care about immigration. In fact polling shows one of the main reasons Biden won was a suburban white reaction to harsh anti-immigrant rhetoric from Trump.