Before revision:  Due to the risk of such supply relationships being idiosyncratically disrupted, firms multisource inputs and strategically invest to make relationships with suppliers stronger. Aggregate production is robust to idiosyncratic disruptions.
After revision:  Due to the risk of such supply relationships being idiosyncratically disrupted, firms multisource inputs and strategically invest to make relationships stronger, trading off the cost of investment against the benefits of increased robustness. We find that equilibrium aggregate production is robust to idiosyncratic disruptions.