We’d like to increase the width where this happens.

You will find the main CSS that shows/hides the menus in your
\fortuna\stylesheets\grid_responsive.css and you can move those around in the different breakpoints.
It’s not advisable though, as there’s other logic associated with Menus that is hooked to WP’s internal checks for mobile devices etc.

Are your menu items too many? May I see your URL, please?

http://www.banksocal.com/

At around 1280 pixel browser width, the menu goes to two lines and expands.

The client isn’t happy with this.

The two problems we have are the logo is too large and the menu items “Business Banking” and “Personal Banking” take up too much vertical space. The menu should really be redesigned but we just launched the site and don’t have time to do that.

However easiest solution is to bring in the mobile menu at 1280. How do I adjust ALL the logic so it works properly at 1280?

@media only screen and (min-width: 1018px) and (max-width: 1280px) {
#logo {
    max-width: 164px;
}
#menu > ul > li > a {
    padding-left: 7px;
    padding-right: 7px;
}
}

Let me know if those fix up things!