A key Senate Democrat

Menendez, first appointed to the Senate in January 2006, is the top Democrat on the Senate Foreign Relations Committee, and a former chair of the Democratic Senatorial Campaign Committee. He has recently been pressuring the Obama administration to toughen Iran sanctions, and has harshly criticized Obama's recent deal with Cuba. He was also part of the bipartisan Gang of 8 that put together the Senate's immigration reform bill in 2013.

It's been clear that the FBI was looking into Melgen for some time. The New York Times ran a series of articles about the relationship between Menendez and Melgen in early 2013.

However, there's been a dispute about whether two of Menendez's aides could be compelled to testify in court. Now, Perez reports, prosecutors are "under pressure" to bring charges "in part because of the statute of limitation on some of the allegations."