There's news of a concerning development involving a possible threat to congressional offices, as well as other addresses nationwide. 

According to the FBI, they are now investigating letters "containing suspicious substances that were mailed nationwide, including to some congressional offices on Capitol Hill. 

“The FBI and U.S. Postal Inspection Service are investigating a series of suspicious mailings sent to various addresses nationwide, including Secretary of State offices and their related election offices. Some of the letters contained an unknown substance and we are working closely with our law enforcement partners to respond to each incident. We are also working with our partners to identify the individual or individuals responsible for the letters. This FBI will continue to safeguard the public and secure elections for American citizens.”

A Senate email said that law enforcement officials were "working to intercept any additional letters before they are delivered; however, it is possible that some letters may reach their destinations." 

The Ohio Secretary of State said it was one of the intended recipients, but the letter was stopped by the U.S. Postal Service.  

According to NBC, Louisiana also got one. 

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“As we have each stated in the past, threats against election officials and workers have no place in our democracy. Those who administer our elections should never fear for their safety while carrying out their essential duties,” the National Association of Secretaries of State and the National Association of State Election Directors said in a joint statement.

“Election officials take these matters seriously and work closely with law enforcement and security partners to protect their personnel and facilities,” the statement added.

Ohio Secretary of State Frank LaRose on Wednesday echoed the sentiment that election officials should “never have to fear for their personal safety while performing their duties,” adding that his office was working with state and federal law enforcement following the mailing targeting it.

The NY Post reported there was a return address on one of the envelopes. 

The FBI, US Postal Inspection Service and Capitol Police are investigating letters “containing suspicious substances” that were mailed to congressional offices, according to emails sent to Hill staff Thursday.

The warning included a photo of one of the suspicious envelopes that was postmarked “DSA” and gave a return address at the same Financial District building that the Democratic Socialists of America used to list on their membership forms.

However, the Democratic Socialists of America responded that they were no longer at that address.