(CNN) Two Democrats leading the rebellion against Nancy Pelosi were bullish Tuesday evening about their efforts to stop her from winning the speakership, promising to soon reveal that they had enough support to cause a major shake-up at the top of their caucus.

The Democrats, Reps. Seth Moulton of Massachusetts and Filemon Vela of Texas, contended that their private conversations revealed that Pelosi would soon learn that she lacked backing within the full House to be elected speaker next year -- despite her confidence that she would lock down the necessary support.

"I am 100% confident we can forge new leadership," Vela told CNN.

Asked how confident they were that they could defeat Pelosi, Moulton also said: "100%."

The Pelosi detractors are circulating a letter and trying to accumulate enough signatures to showcase the breadth of the Democratic opposition to Pelosi. The strategy is this: Show that the California Democrat lacks support after new and current members commit to voting for another candidate on the floor. At that point, they hope, Pelosi will see the writing on the wall, step aside and allow new candidates for the speakership to emerge.

"We are trying to do the right thing for the party by solving this ahead of time," Moulton said.

The goal, they said, is to release their letter as soon as this week or at least before the Nov. 28 leadership elections in the House Democratic Caucus. Pelosi will have to win a majority of support within the caucus to be nominated as speaker -- something that is virtually assured -- before the full House votes for a speaker in January, where the numbers will be critical.

Supporters of Pelosi are deeply skeptical about her critics' predictions, expecting she will get enough votes to become speaker and will overcome the opposition from the small minority of rabble-rousing Democrats. No candidate has emerged to take her on, with even her opponent after the 2016 elections, Rep. Tim Ryan of Ohio, saying he had no plans to jump in at the moment.

"Leader Pelosi is very confident in her support among members and members-elect," said Drew Hammill, her spokesman.

For days, Pelosi herself expressed no doubt she'd be elected speaker.

"A hundred percent," she said on CNN last week when asked about her level of confidence.

Rep. Hakeem Jeffries of New York, whom many Pelosi detractors want to run for speaker, said he believes Pelosi will get the 218 votes she needs -- and insisted he was focused on his race for Democratic Caucus chairman, rather than a bid for the speakership.

"Never count out Nancy Pelosi," he said. "Nobody within the Capitol dome is a better vote counter than the once and future speaker of the United States House of Representatives."

Meanwhile, Rep. Marcia Fudge, a vocal Pelosi critic, said she's not ruling out a potential challenge against the Democratic leader.

"I have ruled out nothing," she said, adding that she's getting encouragement to run from "a number" of people. "But what I'm saying to you is I haven't really given it any thought."

The current split in the House next year is 225-200, with Democrats holding the advantage, and with 10 races still outstanding, it's very likely that the Democratic majority will still grow. According to a CNN tally, 10 incoming freshman have said they'd oppose Pelosi, while 13 incumbents have vowed to oppose her.

But it's unclear if those members might vote against her in the caucus yet vote for her on the House floor. After the 2016 elections, 63 Democrats opposed Pelosi in the leadership races but nearly all of them voted for her later on the floor.

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After this month's vote, the Democratic candidate for speaker will face off against the Republican candidate for speaker in January. House rules say the candidate who wins the race must secure a majority of votes from the members who attend and actually cast votes for a candidate. So if members skip the vote or decide to vote "present," that would lower the threshold below 218 to win the speaker's election, something that could help Pelosi if her critics decide to skip the vote rather than vote against her.

Moulton and Vela insisted that none of the detractors would do that.

"I'm confident that at this point, we have a number of current and incoming members committed to going to the floor and voting for someone else and not voting present," Vela said.

This story has been updated with additional comments from lawmakers.