Does party support help candidates win?

•Party support improves House challengers' but not open-seat candidates' vote margins•Parties' independent expenditures do not improve challengers' competitiveness.•Party support provided after Labor Day contributes the most to challengers' success.

The parties’ congressional campaign committees have made it their business to strategically provide contributions to candidate campaigns in order to help their candidates win. However, the effectiveness of these contributions in terms of increasing the competitiveness of party-sponsored candidates remains untested. Using contribution data from the U.S. Federal Election Commission in a series of mixed effects models as well as a matching analysis, the receipt of direct party contributions and coordinated support is shown to significantly improve the competitive position of challengers but not open seat candidates in races for the House. Further, independent expenditures by the parties do not significantly increase candidates’ competitiveness. The implications of these results for future party strategies are explored.