Final answer:
The informal qualification becoming increasingly important in recent congressional elections is the candidate's ability to fundraise, as it enables extensive campaigning and demonstrates viability.
Step-by-step explanation:
In recent congressional elections, the informal qualification that has increased most in importance is fundraising ability. This is supported by the observation that campaign managers recognize the necessity of securing early funds to disseminate the candidate's information and encourage voter turnout. As more money is raised, it typically results in the capacity to gather even further donations, indicating the candidate's viability. Moreover, entities like EMILY's List have been founded on the concept that early financial support can propel a political campaign and attract subsequent contributions, emphasizing the critical role of fundraising in modern elections.