Gabby Giffords and Mark Kelly offer their thoughts on the fourth anniversary of Tucson's mass shooting:

Four years ago today, at a Safeway in Tucson, Arizona, we lost six members of our community to a senseless act of gun violence. Thirteen others were injured that day.

They were friends and neighbors, colleagues and a young child. We came together and mourned ... and eventually, we began to recover.

Two years later, shortly after the massacre at Sandy Hook Elementary School, we decided that we must act to make our communities safer from gun violence — that it was time to "Do something," Gabby said, "Not just talk."

So on the two-year anniversary of the shooting in Tucson, we started Americans for Responsible Solutions. And we would have never guessed that since that day, over 800,000 Americans would transform our message of responsible gun ownership into a national movement.

Together, we've won victories in State Capitals and Congress. And in Washington State this November, where background checks were on the ballot and won, we created a model that will change our gun laws in states across the country.

We've said before, that in many ways, this effort has a lot in common with a difficult rehab. It's formidable and frustrating work, but once you master an action, it gets easier to repeat.

We'll learn lessons from our victories and repeat them, friend, and that's only possible because we're in this together.

So, today — on the anniversary of our organization's founding — we recorded a video about our shared commitment to each other to see this work through.

We've all known this work would be challenging and filled with ups and downs that test our patience and test our willingness to persevere.

We know something about that, but we're in it for the long haul. Thanks for being there with us.