Custom post type not showing in WP_Query loop

I’m using the Custom post types UI plugin and have written a loop to iterate through these posts. I can’t get my posts to show up even though I have confirmed they exist. I’m not entirely sure what’s missing here and any help would be much appreciated.

Here is my code:

<?php 

            $args = array(
                'post_type' => 'portfolio'
            );
            $the_query = new WP_Query($args);

        ?>

        <?php if (have_posts()) : while ($the_query->have_posts()) : $the_query->the_post(); ?>

        <div class="col-sm-3 portfolio-piece">

            <p><?php the_post_thumbnail('medium'); ?></p>
            <h3><?php the_title(); ?></h3>

        </div>

        <?php endwhile; endif; ?>
        <?php wp_reset_query(); ?>