Pulling Twitter RSS feed not working as expected (fatal error)

I’m trying to get some of the latest posts from a Twitter account, without a plugin. According to Botcrawl.com’s tutorial, this should be enough:

<ul>
<?php
include_once(ABSPATH . WPINC . '/feed.php');
$rss = fetch_feed('https://api.twitter.com/1/statuses/user_timeline.rss?screen_name=BarackObama');
$maxitems = $rss->get_item_quantity(4);
$rss_items = $rss->get_items(0, $maxitems);
?>

<ul>
<?php if ($maxitems == 0) echo '<li>No items.</li>';
else
// Loop through each feed item and display each item as a hyperlink.
foreach ( $rss_items as $item ) : ?>
<li>
<a href='<?php echo $item->get_permalink(); ?>'>
<?php echo $item->get_title(); ?>
</a>
</li>
<?php endforeach; ?>
</ul>

However, I get the following error:

Fatal error: Call to undefined method WP_Error::get_item_quantity() in /Users/username/Desktop/journal_wp/wp-content/themes/Journal_theme/index.php on line 155

Has anyone had any experience with this, and know why it is calling a fatal error?