To be considered compelling an assurance case should address its potential deficits, possibly with the use of a confidence argument. Assurance argument and confidence argument should be clearly separated and consistent at the same time. We propose a way of their integration with the use of an element representing rationale for each argumentation strategy. The rationale integrates confidence argument for a given argumentation step and can be used to demonstrate strength of the argument. The approach is illustrated with a confidence argument development case study. The confidence argument has been created for defeaters identified with the use of a checklist.