Former Democratic Ohio Congressman Tim Ryan tells TMZ ... the American people are realizing it's not realistic to move forward with President Biden after the commander-in-chief's disastrous June 27 debate against Trump -- his Republican rival. Instead, many dems are beginning to recognize that Kamala is their path forward.

"She is the only candidate [because] she is VP and on the ticket with him that will inherit his war chest and campaign infrastructure," according to Ryan, who lost reelection to J.D. Vance in 2020 after more than 20 years in office.

Ryan says he's been talking with members of Congress, Senate offices, and other major players in the democratic party -- and all are yearning for unity, reconciliation and government reform, which, they believe, Kamala can deliver on as president.

Trump, however, sees a potential battle with Kamala for the presidency as a huge victory for him. His campaign spokesperson, Karoline Leavitt, informed us Kamala performs worse than Biden in some of the head-to-head polls against Trump.

Leavitt cited a poll that showed Trump beating Harris by 7 points -- 49 percent to 42 percent with 9 percent undecided. The same poll revealed Trump winning by 5 points over Harris when factoring in RFK Jr., Jill Stein and Cornel West. By contrast, the latest New York Times/Sienna College poll has Trump leading Biden by 6 points.

Leavitt put it this way to TMZ ... "The Democrats are in a no-win situation. If they stick with Biden, they lose. If they switch to Kamala, they lose even by more. President Trump is going to win no matter what they decide."

But, Ryan doesn't see it like that ... the ex-congressman said Kamala would shift the dynamic of this race back to the dems by bringing in fresh enthusiasm and bolstering their support with minorities.

Ryan says he campaigned with Kamala in 2020 when he launched his failed bid for the White House --- and she knows how to connect with people. In other words, Kamala's a total rock star.

Ryan also noted Biden has a long history of trying to do the right thing for the country so he thinks it's possible Joe will make the correct decision and withdraw from the race to pave the way for a younger generation of democratic leaders, starting with Kamala.

Meanwhile, earlier this week, a panicked Democratic official told us it's only a matter of time before Biden bows out and Kamala likely replaces him.

The source likened Biden's probable exit to a "money thing," explaining the funds he raised were earmarked for the Biden/Harris campaign. There's now a serious question about whether that money would be available to another candidate, which dovetails with what Ryan said about Kamala inheriting Biden's war chest.