“It’s not just about being an activist,” Ms. Ocasio-Cortez said. “It forces you to grow. So it doesn’t mean you don’t endorse activists, but it also requires an assessment for a capacity of growth and how you navigate a space like this.”

When she first arrived on Capitol Hill, Ms. Ocasio-Cortez and her team made it clear they planned to use their perch inside Congress as a platform for their divisive, outsider brand of politics. On her first day of orientation, Ms. Ocasio-Cortez joined protesters camped outside Speaker Nancy Pelosi’s office agitating for the Green New Deal.

“It could have made people mad; they could have put me on the dog walking committee,” she joked later that week on a Justice Democrats conference call promoting the organization’s candidate recruitment campaign. “They still might.”

Ms. Ocasio-Cortez may have meant it as an offhand quip, but her comment underscored a reality on Capitol Hill that she and her team were slow to fully appreciate: the extent to which power and the ability to get things done in the House were dependent on personal relationships and respect for the hierarchy.

The first-term congresswoman enjoys rich public support outside Congress, particularly on the social media platforms where progressive activism thrives. But the approach that she and her cohorts champion — pulling the institution to the left in part by threatening the careers of any Democrats who fail to embrace their ideas — quickly alienated many of her colleagues, and has made it difficult for her to get anything done.

In private conversations, many of Ms. Ocasio-Cortez’s Democratic colleagues routinely complain that in her zeal to build her social media celebrity and political brand, she is too quick to cast aspersions on her fellow lawmakers, painting them as apologists for the status quo.