What factor is often a key indicator of a union's organizing success rate?

Support shown by the union's membership is a key indicator of a union's organizing success rate because strong membership support reflects a collective commitment to the union's goals and initiatives. When members actively participate in organizing efforts, it enhances the union's ability to advocate for workers' rights, negotiate effectively with employers, and mobilize against opposition. This solidarity can attract new members, bolster existing campaigns, and demonstrate to potential members and employers that the union has a robust backing among its ranks, increasing the likelihood of successful organizing campaigns.

In contrast, while financial resources can provide essential backing for organizing efforts, they do not guarantee success if the membership is not engaged. Membership growth is a positive outcome that can result from successful organizing but is not, in itself, an indicator of success. Lastly, training programs offered by the union are beneficial but do not directly reflect the level of active support and commitment from the membership towards organizing initiatives.