It's not hard to share the frustration that has led Steve Bannon to promise to primary every Republican senator up for re-election in 2018 (except for Ted Cruz).

It's not hard to understand why Bannon is fed up with Senate Majority Leader Mitch McConnell, R-Ky. McConnell has had seven years to figure out how to repeal Obamacare, and he still can't get that or tax reform or anything else across the finish line. He seems unable to corral his members and unwilling to truly do the work required to drain the swamp, and he's pretty clearly not a close friend of the administration despite his recent public kumbaya.

It's not even all that hard to understand why Bannon would try to clean house – even going after octogenarian Sen. Orrin Hatch, R-Utah.

But what is hard to understand is exactly what problem Bannon seeks to solve with this purge. The Republican senators up for election in 2018 have not been the dam blocking Trump's agenda. Indeed, all voted with him on every iteration of Obamacare repeal, and all but one have voted with him at least 91 percent of the time.

In fact, Jeff Flake of Arizona, who already is in trouble in his primary, may not always have had favorable things to say about Trump, but he's voted with the president 91.7 percent of the time. John Barrasso of Wyoming, Orrin Hatch of Utah and Roger Wicker of Mississippi, all targeted by Bannon, have voted with Trump nearly 96 percent of the time.

Meanwhile, the senators who did vote against him at key times – Susan Collins of Maine, John McCain of Arizona, Rand Paul of Kentucky and Lisa Murkowski of Alaska – are not up for re-election in 2018.

As Jim Geraghty wrote in National Review, "Trump doesn't need different GOP senators, he needs more of them." He needs enough to not have to worry about defections. He needs enough to not have to pass every big piece of legislation through the budget reconciliation process, which requires only 50 votes rather than 60 but comes up only once per year.

Attempting to dump senators who provide reliable votes for the Trump agenda seems like a counterproductive strategy. You could end up with someone such as Roy Moore, Republican nominee for Senate in Alabama, who essentially appeals to a lot of the same voters as Trump. He may win a squeaker, but then again it is the reliably red Yellowhammer State.

But you may end up with candidates not quite so ready for prime time. Past standout gems include Christine O'Donnell and her spirits in Delaware, Todd Aiken and his strange views on rape in Missouri, and Richard Mourdock, who couldn't avoid the Aiken trap in Indiana. All knocked off Republican candidates who could have won, then committed gaffes that took themselves out of the race.

This seems a curious time to upend the apple cart. Republicans are gaining momentum, and senators are voting with the president. Moreover, 10 Democratic senators are up for re-election in states that Trump carried in 2016. Cook Political Report has Joe Donnelly of Indiana, Claire McCaskill of Missouri and Joe Manchin of West Virginia as toss-ups, and Florida's Bill Nelson, North Dakota's Heidi Heitkamp and Ohio's Sherrod Brown as only "Leans D."

A decisive run by disciplined, well-trained, and vetted candidates could yield a huge harvest for Republicans in 2018. Bannon supposedly knows what is at stake and has pledged to find competent, well-financed candidates who are dedicated to two things – enacting the president's agenda and getting rid of McConnell as majority leader. Only time will tell, but Bannon has his skeptics.

Even if he pulls it off and replaces current loyalists with Trump purists, what message, Gerhaghty asks, does this send to the other senators?

In some cases, presumably, it won't matter because they will be routed from office by the Bannon-backed challenger. But in most cases, they will win and return to the Senate, where they have voted with the president more than 90 percent of the time (far more for some) but will have had to spend millions of dollars to fight off challengers seeking to punish them for not being stricter adherents to the president's agenda.

Bannon is right that Trump is a powerful political brand – perhaps the most powerful of our lifetimes. People voted for him because they voted for a certain attitude toward governance, and they don't see that coming from even those 96-percenters in the Senate.

But before he can truly advance Trump's agenda, Bannon needs to be cognizant of the need to protect it. After all, if enough dumpster fire candidates get involved this time, Chuck Schumer or someone worse will be handling the Senate gavel, and nothing Trump supports will pass.

And that would be monstrously frustrating, particularly if the GOP can't hold the House too.

Ford O'Connell (@FordOConnell) is a contributor to the Washington Examiner's Beltway Confidential blog. He is an adjunct professor at The George Washington University Graduate School of Political Management, worked on John McCain's 2008 presidential campaign, and authored the book "Hail Mary: The 10-Step Playbook for Republican Recovery."

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