At their first rally together, Democratic presidential candidate Hillary Clinton spoke about Sen. Elizabeth Warren (D-Mass.), as a champion of working class families. Clinton is vetting Warren as a potential vice presidential nominee. (Reuters)

Elizabeth Warren has been the subject of vice presidential speculation for months, but the media has generally downplayed the likelihood that she will join Hillary Clinton on the Democratic ticket.

A Politico story in April, for example, threw cold water on "the Clinton-Warren fantasy." Under the headline "Why Hillary Clinton won't pick Elizabeth Warren for VP," Newsweek in May outlined four top reasons, including a lack of chemistry. Just last week, the New York Times published a story with a nearly identical — but slightly less definitive — headline: "Why Hillary Clinton probably won't pick Elizabeth Warren as a running mate." Fix Original Recipe Chris Cillizza doesn't think Warren is a match for Clinton, either.

But as the Massachusetts senator joined the presumptive Democratic presidential nominee on the campaign trail for the first time Monday, journalists seemed to be watching and thinking, "This could really happen."

To be clear, one event didn't erase all skepticism. The Huffington Post's Jess Coleman, who has argued in favor of Tim Kaine as Clinton's running mate, summarized the thinking of many Warren-VP doubters in a series of tweets.

Still, on a day when ABC News reported the Clinton campaign has intensified its vetting of Warren, the joint appearance in Cincinnati had journalists buzzing about how naturally the senator fits into the role of sidekick/attacker-in-chief.

"There’s no question she’s mastered one aspect of the job: attack dog," Michael A. Memoli wrote for the Los Angeles Times.

Sen. Elizabeth Warren (D-Mass.) is on Democratic presidential candidate Hillary Clinton's short list of potential vice presidential candidates. Here's what you need to know about her. (Sarah Parnass,Osman Malik/The Washington Post)

Bloomberg's Jennifer Epstein described Warren's remarks in Ohio as a "scathing attack on presumptive Republican nominee Donald Trump."

It should be noted that these are the same reasons why Warren's selection by Clinton would be so much fun for the media. She goes after Trump in Trump-ian ways that Clinton dares not attempt — blasting him on Twitter and even mocking his appearance.

"You wanna see goofy? Look at him in that hat," she told the crowd on Monday.

Warren has become the media favorite — not in the sense that she is considered the front-runner to be Clinton's No. 2 or even that the media supports her politics, but in the sense that she is the best story. Virtually unknown only five years ago, she captured national attention by unseating Republican Sen. Scott Brown (R-Mass.) — seen at the time as a rising star — in 2012. In office, Warren has quickly become a leading liberal voice, not to mention a reliably colorful quote.

Kaine, meanwhile, is "boring" — and that's how he describes himself.

Warren on the ticket would ensure a summer and fall of fiery rhetoric and, as a result, must-click headlines. As her veep stock rises in the press, wishful thinking might be helping to drive up her perceived prospects.

Whatever the reasons, it appears that Warren is moving from long shot to real contender in the eyes of the press. The practical arguments against her selection remain unchanged, but the energy she brought to the stage in Cincinnati — an intangible that many journalists have found lacking at Clinton events — was widely noted.

For the Clinton campaign, the media's reaction is one way to measure the success of this Warren trial balloon. The signal from the press is that Warren's enthusiasm might be enough to make up for her risks and lack of Clinton loyalty in the past.