Democrats are facing a wave of primary challenges from younger, more progressive candidates frustrated with how the party is confronting Trump. Incumbents say the infighting wastes money and energy needed to beat republicans, while challengers argue democrats need bolder leadership. party leaders expect most incumbents to survive but the battles highlight a growing divide over the partys future.

As the immune system weakens with age, scientists have found a way to restore some of its lost strength. By delivering mRNA to the liver, they created a temporary source of immune-boosting signals that normally come from the thymus. Older mice treated this way produced more effective T cells and responded far better to vaccines and cancer treatments. The strategy could one day help extend healthy years of life