Biden should provide evidence he can beat Trump, Democratic leaders say
It seems you're referring to a statement from existing members of the Democratic Party asking President Biden to prove his competitiveness against former President Trump. In the context of politics, proving one's ability generally comes in terms of successful implementation of policies, good diplomatic relations, effective crisis management, favorable approval ratings, etc.
However, since each political situation is unique, there might be other criteria too, depending on the specific issues that are prevalent at the time.
It is also important to understand that not all members of a political party agree on everything and these statements might represent a fraction of voices within the wider Democratic leadership. This is a common occurrence in political parties where internal debates and discussions are an essential part of the democratic process.
If you are interested in more detailed and specific news, I would need more context or more specific information. For example, who made this statement, when, why, and what specific evidence they want Biden to show. I can then provide more detailed information based on these specifics.