The phrase "to shore up" means to strengthen or support something that is weak, failing or in danger of collapsing. It can be used both literally and figuratively. In a literal sense, it refers to adding sandbags or other supports to prevent erosion along the shoreline. Figuratively, it means to reinforce or stabilize an idea, belief, plan, or situation that is in danger of falling apart. For example, if a political party's popularity is declining, they may try to shore up their support by implementing new policies or making changes to their leadership team.