Arizona’s senior senator is drawing the ire of party officials both in D.C. and back at home over her refusal to destroy the Senate’s filibuster rule and her unwillingness (at least for now) to go along with Democrats’ plans for a $3.5-trillion spending bill chock full of progressive wishlist items. The Arizona Democratic party approved a resolution bashing Kyrsten Sinema over her positions on the filibuster and the reconciliation bill over the weekend, warning her that vote of no confidence is coming unless she changes her ways and falls in line.

There’s one Arizona Democrat who isn’t saying much at all about Sinema, however. Her Senate colleague Mark Kelly, co-founder of the gun control group Giffords and a Democrat who was elected to the Senate in a special election last year, has been keeping awfully quiet, not only about Sinema’s positions but his own as well. And in Arizona, Republicans are watching and taking note.

Unlike the other Democratic senator in Arizona, Sen. Mark Kelly isn’t causing trouble for party leaders, saying he is focused on state issues. Republicans argue his stance gives them an opening to unseat him when he seeks re-election next year.

Mr. Kelly last year narrowly defeated a Republican appointee to win the remainder of the late GOP Sen. John McCain’s Senate term in the swing state. His 2022 race is seen as one of the top pickup opportunities for Republicans and could decide which party controls the U.S. Senate, currently split 50-50 but controlled by Democrats.

The former Navy pilot and astronaut followed in the footsteps of Sen. Kyrsten Sinema, who won an open seat in 2018, becoming the state’s first Democratic senator in three decades. Both won by 2.4 percentage points.

Ms. Sinema has sometimes crossed party leaders and regularly angered the party’s progressive wing with her stances on federal spending and the filibuster, the rule requiring 60 votes to advance most legislation. But Mr. Kelly has avoided such clashes, while airing some differences with the White House on issues such as border policy.

“My approach is working across the aisle, and pushing back against the administration when I think it’s the appropriate thing to do, when I don’t like what I’m hearing from the White House,” he said in an August interview. “I’m going to make decisions based on what I feel is in the best interest of our state and our country, regardless of the politics.”

Kelly’s been keeping his head down, which might be the safe play politically in a purple state like Arizona, but as the Wall St. Journal points out, it also provides an opening for Republicans, who can point to the fact that unlike Sinema the state’s newest senator is toeing the party line while claiming to be an independent-minded politician.

“He promised to be independent and instead he’s voting with Chuck Schumer, ” the Senate Majority Leader, said Blake Masters, a top aide to billionaire investor Peter Thiel running for the GOP nomination to take on Mr. Kelly. “Sen. Sinema is actually way more interesting,” said Mr. Masters, pointing to her opposition to ending the filibuster.

“I think she just shows how dyed-in-the-wool Mark Kelly is for the progressive agenda,” he said.

Democrats counter by claiming that there’s not much difference between the two candidates politically, which is probably the case when it comes to things like support for gun control. There’s a huge difference, however, in how the two approach issues like the filibuster. Sinema has been outspoken about not changing the Senate rules to allow legislation to pass with just 51 votes, while Kelly has largely been silent, at least publicly. In private, however, he’s called for “changing the rules”.

At one point, an attendee asked Kelly what he planned to do to get Sen. Kyrsten Sinema — Arizona’s other senator — and West Virginia Democrat Sen. Joe Manchin “to end the filibuster” and allow for Democrats to have a “functional majority” in the Senate.

“Yeah, sir, certainly we need a change. We’re not we’re not going to keep doing the same thing and get a different result,” Kelly responded. He added: “There’s no other democracy, as far as I know, that works the way the United States Senate does. So structurally, it’s got major issues. I would like to see us, you know, change the rules.”

Change the rules so he can change the laws; particularly the laws regarding our right to keep and bear arms. There’s no way that Kelly gets any of his anti-gun agenda through Congress with the filibuster in place, but he also doesn’t want to appear to be too far to Sinema’s left, particularly when he’s up for a full six-year term next year. So he’s working behind the scenes to erode the filibuster while publicly portraying himself as a middle-of-the-road Democrat. That strategy may work to his advantage in the Democratic primary next year, but with Joe Biden’s approval rating tanking, I suspect that Kelly’s going to be in for a much tougher fight in the general election.