Earlier this week, Senator Elizabeth Warren announced a sweeping set of anti-corruption proposals to a crowd of supporters in New York City's iconic Washington Square Park. The focus quickly shifted to the sheer size of the rally — estimated at more than 20,000 — and what that means for the narrowing field of 2020 Democratic contenders. But as CBS News special correspondent and co-host of "The Circus" Alex Wagner observed, the event was significant for more reasons than the number of attendees.

"You saw her framed under Washington Square Park arch with her campaign signs flanking her. That was a bid to show America, to show undecided Democrats that Elizabeth Warren can be a stateswoman. That she can be the kind of person that can lead the country," Wagner told "CBS This Morning" on Friday.

Warren has emerged as one of the top Democratic presidential contenders in recent weeks, but Monday's event revealed a new strategy that, as Wagner pointed out, is widely seen by Democrats as the best bet for defeating President Trump.

"Elizabeth Warren wants to plant her flag in this anti-corruption strategy. It's something all the Democrats want to use against Trump, but she wants to own it," Wagner said. "And if you look at the polling around Warren, you see momentum there. That rally only helped with that."

Though she has picked up momentum, the Massachusetts senator is still polling closely to fellow 2020 contender Bernie Sanders and, at the end of the day, there can only be one Democratic nominee.

"If you talk to Warren supporters, it's really interesting. They like Warren — they don't want to alienate Bernie Sanders supporters in their support for Warren. They don't want to even alienate Biden supporters. There's a sense inside the Democratic voting caucus that, look, we have favorites, but we will get behind whoever the winner is and within the Warren campaign and the Sanders campaign, you hear that echoed publicly," Wagner said.

But there is a sense, according to Wagner, that a two-way race rather than a three-way race could soon emerge.

"I think this week you heard frustration from the Sanders campaign. Elizabeth Warren got a coveted endorsement from the Working Families' Party. That polling shows her having momentum. There's a sense that this thing is really narrowing and could be a two-way race rather than a three-way race. And you're hearing frustration from the Sanders campaign on Twitter and at the actual events. Warren, meanwhile, I think understands that her path to victory involves bringing those Sanders voters into the fold so she has more of a magnanimous, I think, message, more broadly, and even quietly. There's a sense that they cannot win over Sanders' supporters by alienating them. But no matter where you go, I cannot underscore enough the sense of trepidation among Democratic voters. There is real fear that they've got to rally behind their nominee to defeat Donald Trump because that's the existential threat."