Democrats are proposing several measures to boost security at airports, train stations and other transportation hubs in response to terrorist attacks in Brussels and elsewhere.

Democratic senators outlined proposals Tuesday that would double the number of government "viper teams" that stop and search suspicious passengers in public areas prior to screening, often using bomb-sniffing dogs. They also want more federal grant money to go to training law enforcement officers in how to prepare for and respond to shootings at vulnerable targets such as transportation hubs.

They plan to offer the proposals, including a bipartisan bill that would tighten the screening of airport workers, to an aviation policy bill being considered by the Senate.