Many article databases will allow you to just search just the editorial/commentary sections. For example:
Check database Help screens for more information if you need guidance.
Also use Political Perspectives in Periodicals to help determine what stance (liberal, conservative, etc.) many popular periodicals often take.
Background and reference sources:
Breaking news can be tracked using wire services and newspapers. As news is breaking, conflicting stories and new information can emerge, so it is important to try stay on top new developments and understand how to crtically read the news.
See the Breaking News Consumer Fact Book by NPR for what to look for when following developing news.
Sometimes, it is important to understand how the news coverage of a topic unfolded. In addition to searching through newswires and social media - both which often allow early coverage to leak out before news stories are fully verified, you can also try seeing how website coverage of an even changed over time.
In cases where there has been grassroots/community development, blogs and other social media can help a researcher track both an event as it develops and popular interest in the event.
If you use a blog aggregator or reader for rss feeds, it might also have a built-in search function that allows search for blogs and sites that have rss feeds that can be used to search for posts or blogs by topic.
Using advanced search screens of search engines to limit to specific domains is another way to search blog sites such as wordpress, tumblr, blogger, etc.