Arizona Rep. Ruben Gallego (D)

Oh nuts to this. Sophomore Rep. Ruben Gallego has not only been a rock-solid progressive during his tenure in Congress, he's also emerged as one of the fiercest and most outspoken critics of Donald Trump in the entire Democratic Party. So what has that earned him? A primary challenge from a state senator, Catherine Miranda, who claims to be a Democrat but is awfully cozy with the GOP—so cozy that she endorsed Republican Doug Ducey when he successfully ran for governor in 2014.

And that's not all—far from it. Gallego's campaign greeted Miranda's entry into the race by dubbing her "an anti-choice, corporate-sponsored politician," and she certainly is anti-choice. Among other things, she voted to ban abortion at 20 weeks, voted to defund Planned Parenthood, and even signed a "pro-life pledge." She also launched her campaign by promising to be "someone who will put partisan politics aside, and get things done," a message that couldn't be more out-of-step with our times. At least we can be confident that few Democratic primary voters will find that sort of talk appealing.

But Miranda still poses a deeply frustrating problem for progressives, particularly because the sort of wealthy Republican donors who remember her support for Ducey would likely be all too happy to help her kneecap a rising star like Gallego. Arizona's primary also isn't until the end of August, meaning this race could become a distraction even as we enter the stretch run ahead of the midterms. Fortunately, Democrats won't have to worry about the general election here, since the Phoenix-based 7th District went for Hillary Clinton by a heavy 72-23 margin, but the last thing we'd want is to see someone as awful as Miranda replace someone as awesome as Gallego.