John – I've dedicated my life to service: as an astronaut, an engineer and a U.S. Navy captain. And now, I'm officially the Democratic candidate to be the next senator from Arizona.

That's why my friend Catherine asked me to reach out to her grassroots team for help in taking on this mission – because no one can win a race this big alone.

I'm running because we need to end the outrageous influence corporate PAC money has on our politics – influence that slows our progress on everything from ensuring affordable, accessible health care to tackling climate change.

I know this won't be easy: Our race is being called one of the Democrats' best opportunities to pick up a Senate seat, and Mitch McConnell and Senate Republicans won't go down without a fight. They've pledged to spend more than $20 million to keep this seat red – and the Senate Republican campaign arm has been running TV ads attacking me, which I'm sure will be the first of many before Election Day.

But I also know we can win. A recent poll shows us tied with our opponent, and bit by bit, we're continuing to build one of the strongest grassroots campaigns anywhere. Now election experts are ranking Arizona's Senate seat as one of the seats most likely to flip.

This campaign is powered by grassroots supporters like you, John – and with our midnight fundraising deadline just hours away, I'm relying on you to help us hit our goal.

So, as one of Catherine's biggest supporters, will you please chip in to support our campaign and take back the Senate? You can use this link: secure.actblue.com/donate/ccm4mk

Together, I know we can win in Arizona and flip the Senate.

Full speed ahead,

Mark