Plagiarism: MAYBE, copyright violation: YES.
If an article doesn't have a Creative Common License, then the article owner could issue a DMCA takedown notice.
IMO, verbatim copy paste should be avoided with or without the link to the source except you want to make a point about some specific part of the article.
Edit: this is good info https://www.lifewire.com/copyright-on-the-web-3466815