PHP MySQL JQuery form doesn't validate on client side

I have a simple contact form that posts to MySql on submit, I am trying to validate on the client side before submitting the form (I will implement server side validation after I get the client side to work). For some reason when I submit the form it posts to the DB but doesn't fire up the client side validation. Any help would be appreciated.

This is the HTML (twitter bootstrap) code:

<form action="/contact.php" method="post" id="contactUs">
    <div class="control-group">
       <label class="control-label" for="Name">NAME<sup>*</sup></label>
       <div class="controls">
         <input type="text" class="span4" name="name" placeholder="Name" id="name">
         <span class="help-block"></span> 
        </div>
    </div>
    <div class="control-group">
       <label class="control-label" for="Email">EMAIL<sup>*</sup></label>
       <div class="controls">
         <input type="text" class="span4" name="email" placeholder="Email" id="email">
         <span class="help-block"></span> 
       </div>
    </div>
    <div class="control-group">
       <label class="control-label" for="Subject">Subject<sup>*</sup></label>
       <div class="controls">
         <input type="text" class="span4" name="subject" placeholder="Subject" id="subject">
         <span class="help-block"></span>
       </div>
     </div>
     <div class="control-group">
        <label for="textarea" class="control-label" for="Comment">COMMENTS<sup>*</sup></label>
        <div class="controls">
          <textarea rows="5" class="span6" name="comments" id="message"></textarea>
          <span class="help-block"></span>
        </div>
      </div>
      <div class="control-group form-button-offset">
      <input type="submit" class="btn btn-large btn-primary pull-right" value="Send Message" />
     </div>
      <input type="hidden" name="redirect" value="contact_us.html" />

<script src="js/jquery-1.9.0.min.js"></script>
<script src="js/jquery.validate.min.js"></script>
<script src="js/contactUs.js"></script>
<script src="js/bootstrap.js"></script>
<script src="js/bootstrap.min.js"></script>

Below is the code for the contactUs.js:

$(document).ready(function(){
$('#contactUs').validate({
    rules: {
        name: {
            minlength: 4,
            required: true
        },
        email: {
            required: true,
            email: true,
        },
        subject: {
            minlength: 5,
            required: true
        },
        submission_Reason: {
            minlength: 5,
            required: true
        },
        comments: {
            minlength: 8,
            required: true,
        }
    },
    messages: {
        name: "Please enter your first and last name",
        email: "Please enter a valid email address",
        subject: "Please enter a subject",
        comments: "Please enter a short message",
    },
    highlight: function (element, errorClass, validClass) {
        $(element).closest('.control-group').removeClass('success').addClass('error');
    },
    unhighlight: function (element, errorClass, validClass) {
        $(element).closest('.control-group').removeClass('error').addClass('success');
    },
    success: function (label) {
        $(label).closest('form').find('.valid').removeClass("invalid");
    },
    errorPlacement: function (error, element) {
        element.closest('.control-group').find('.help-block').html(error.text());
    }
});
};

and the PHP contact.php file:

    <?php

$con=mysqli_connect("host","username","password","dbname");

// Check connection
if (mysqli_connect_errno())
  {
  echo "Failed to connect to MySQL: " . mysqli_connect_error();
  }

$sql="INSERT INTO contactUs (name, email, subject, comments)
VALUES
('$_POST[name]','$_POST[email]','$_POST[subject]','$_POST[comments]')";

$sql="INSERT INTO contactUs (`date_created`) VALUES (now())";

if (!mysqli_query($con,$sql))
  {
  die('Error: ' . mysqli_error($con));
  }
echo "Your form has been received, Thank you!";

mysqli_close($con);

?>

When I submit the form the client side validation is not triggered and the result is:

• the form gets submitted and posts to DB
• I get: Your form has been received, Thank you!

What am I doing wrong? why isn't the validation happening?