WASHINGTON -- Democrats said Tuesday they will push proposals to boost security at airports, train stations and other transportation hubs in response to attacks in Brussels and elsewhere.

The initiatives outlined by Democratic senators would double the number of government "viper teams" that stop and search suspicious passengers in public areas before screening, often using bomb-sniffing dogs, from 30 to 60. They also want more federal grants to train law enforcement officers in how to prepare for and respond to shootings at vulnerable targets such as transportation hubs and other "soft targets."

Democrats plan to add the ideas to an aviation policy bill under consideration in the Senate, along with a bipartisan measure to tighten the screening of airport workers.

The screening bill, passed by the Senate commerce committee in December, would give the Transportation Security Administration ready access to additional terrorism-related databases maintained by the intelligence community when vetting airport workers. It also would let TSA conduct real-time, continuous criminal records checks through the FBI and expand the list of criminal convictions that would make a potential airport worker ineligible for security clearance.

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Another bill passed by the House last year with bipartisan support that seeks to expand the number of passengers enrolled in TSA's expedited clearance programs is also expected to be offered for inclusion in the aviation bill.

The aviation bill would extend the Federal Aviation Administration's authority to operate, due to expire July 15, through Oct. 1, 2017. It also contains provisions that lawmakers have been working on for more than four years to address aviation issues, including greater access for drones to the national airspace and protections for airline passengers chafing at fees for basic services such as checked bags and ticket changes.

Sen. John Thune, R-S.D., chairman of the Commerce, Science and Transportation Committee, said Tuesday that he would prefer to deal separately with the security proposals. The proposals have wide support and are expected to easily pass the Senate. However, he didn't say he'd oppose their inclusion in the aviation bill.

When Ibrahim El Bakraoui blew himself up in the Brussels Airport check-in area, killing and maiming scores of travelers, it was at least the third time he had passed unimpeded through an airport terminal in recent months.

Suspected by Turkey of being a "foreign terrorist fighter" and known at home in Belgium as an ex-con wanted for parole violations, Bakraoui was still allowed to board a commercial airliner unaccompanied last summer, flying freely from Istanbul to the Netherlands and disappearing without a trace.

The ease with which he did so raises questions about how much governments know about the movements of returnees among the 5,000 home-grown jihadis who have trained and fought in places like Syria or Iraq. Many now pose a "serious threat," according to the police agency Europol. Some, like Bakraoui, have already used their deadly skills in cities like Brussels or Paris.

Testimony from government ministers, extracts of documents and conversations with police, border and aviation officials reveal a series of security gaps, misunderstandings and procedural red-tape that surrounded the deportation last July of this future suicide bomber.

At European Union headquarters in Brussels, meanwhile, new measures to tackle the issue of returning foreign fighters are near completion. These include the IDs of returning EU citizens to be cross checked with police databases and a Passenger Name Record system giving authorities access to travelers' personal information.

It's an open question, though, as to how effective they will be when solid information already in the hands of officials now is not put to good use.