In order to meet WCAG 2.0 accessibility guidelines, websites must be navigable by keyboard only.

WCAG 2.0 guideline 2.1 : Make all functionality available from a keyboard.

For federal government websites, the standard is Section 508 provision 1194.21(a).

To make the Bootstrap 3 framework fully accessible via tab and arrow keys, Paypal has made available a much appreciated Bootstrap accessibility plugin,

This plugin adds accessibility markup to the default components of Bootstrap 3 to make them accessible for keyboard and screen reader users.