Over the last several months, the United States has seen numerous incidents of classified documents having been either mishandled or leaked to the public. Here are three of the biggest examples of this occurring so far this year, and why concern has grown over the government’s handling of mishaps like these.

1. Classified documents at homes of Biden, Trump and Pence

First, there was a bevy of classified files that several members of past presidential administrations had improperly been keeping at their private residences. President Joe Biden, former President Donald Trump and former Vice President Mike Pence were all found to have brought documents back to their homes after their terms in office. The records found in Biden’s Delaware home were from his time serving as vice president in the Obama administration, while the Department of Justice has been probing the classified files discovered at Trump’s Mar-a-Lago residence.

2. Biden security plans on streets of Belfast

Next, local police documents detailing security protocols for Biden’s visit to Ireland were discovered after having been left on a street in Belfast. This came amid heightened security concerns and a rash of political violence in Northern Ireland. The terrorism threat in the area had been raised to “severe” ahead of of the president’s visit. The names, phone numbers and addresses of top Northern Ireland police officers were shared in the found material.

3: Air National Guard member’s intelligence leaks

Meanwhile, most recently, the FBI arrested Jack Teixeira, a 21-year-old member of the Massachusetts Air National Guard, over classified documents that were leaked on the internet. That leak exposed potentially hundreds of pages of intelligence about Russian efforts in Ukraine and spying on U.S. allies. Charging documents reveal that one of the posted documents “described the status of the Russia Ukraine conflict, including troop movements.”

As the government ponders this recent rash of security concerns, CNN’s What Matters newsletter has pointed to the more than 1 million people that currently hold Top Secret security clearance as a possible source of these problems. Information is classified as top secret if it “reasonably could be expected to cause exceptionally grave damage to the national security,” according to a 2009 executive order that describes the classification system.