Could drinking a lot of whiskey make someone more likely to commit suicide or motivate a suicidal person to actually attempt suicide?

Unfortunately, yes: There is significant evidence to suggest any alcohol misuse predisposes to suicidal behavior through its depressogenic effects. The good news is that effective interventions for problem drinking may help reduce suicide rates and improve quality of life. You're not alone; many of us have had suicidal thoughts at some point in our lives. Ask for help! it is widely available.