<nav id="mainMenu" class="navbar">
<div id="navbar-inner pull-left">
<a class="btn btn-navbar btn-mini" data-toggle="collapse" data-target=".nav-collapse">
<p>menu</p>
</a>
<div class="nav-collapse">
<ul class="nav">
<?php wp_nav_menu(array('main_nav' => 'mainNav','container_class' => 'container', 'menu_class' => 'nav',)); ?>
</ul>
</div>
</div>
</nav>
so why isn’t the main nav collapsing?