Paul Kane, The Post's senior congressional correspondent, is also the nation's foremost e-mail writer -- or at least he's close. Every few weeks, PK and I get into an e-mail back-and-forth that I think is worth publishing. We started a conversation Friday debating the on-again, off-again friendship of Senate Majority Leader Mitch McConnell and his Kentucky colleague Rand Paul -- even as it's being severely tested by the ongoing fight over the National Security Agency. Our conversation, edited only for grammar, is below.

FIX: Ok, PK. Congress is enjoying a week-long Memorial Day recess. But, before they left, the Senate went long into the night debating what to do about the future of the NSA’s bulk surveillance program — a sort of proxy fight for the coming vote over re-authorizing the Patriot Act.

That fight, which ended, for the moment, unresolved, boiled down to a battle between two people: Senate Majority Leader Mitch McConnell and 2016 presidential candidate Rand Paul. But they were best friends!

Bring me into that scrap. And what it means.

PKEnemies who developed a bromance, now threatening to crater into frenemies – too much?

Last week was the five-year anniversary of the tea party’s first major win in any major election; that of Rand Paul winning the May 2010 GOP primary over the hand-picked candidate of McConnell. “We’ve come to take our government back,” Paul shouted from the stage that night.

It was very embarrassing for McConnell, who built the modern Republican Party in the Bluegrass State. Every top McConnell adviser that I’ve ever spoken to says that was a crucible moment, when he didn’t know the pulse of his own state’s voters. Convinced Paul could be defeated, even in the last week, McConnell cut an ad for his understudy’s (former Kentucky secretary of state Trey Grayson) campaign. If anything, it backfired.

At that moment McConnell could already see 2014 and his own reelection on the horizon. He spent the next three years trying to learn from it. His top advisers helped Paul win the general election. Still, the early days were awkward. Paul’s first floor speech was an excoriation against Henry Clay, for his role as the “Great Compromiser." McConnell sat ashen-faced as Paul attacked someone he considered Kentucky’s greatest political hero.

But week by week, month by month, they learned to get along and realized that each could learn from the other’s strengths and weaknesses, they could shore each other up, and pretty soon their staffs worked very closely. Before you knew it, McConnell was jamming a hemp provision into the farm bill at Paul’s behest, and he hired Paul’s campaign manager, Jesse Benton, to run his 2014 reelect.

Rand’s street cred with tea party activists was helpful, added with McConnell’s lessons of how to run an overwhelming force campaign against under-funded conservative challengers, led to an easy primary win in ’14. At Kentucky’s annual political gong show, Fancy Farm, in August 2014, McConnell stood in front of GOP activists and favorably compared Rand Paul to . . . Henry Clay.

The final 24 hours of McConnell’s general election campaign last November, consisted of a prop plane, a pilot, McConnell, his wife Elaine Chao and … Rand Paul flying around Kentucky.

But as Paul’s presidential campaign lifted off, Paul has tried to go back to his political roots – Rand 3.0 is really more like Rand 1.0. He frequently lashes out at the “Washington machine," which, if you closed your eyes and thought who represents that machine, a lot of people would see Mitch McConnell.

Paul is again trying to be the leading libertarian on national security, latching onto the re-authorization of portions of the Patriot Act as his biggest issue.

If McConnell is nothing else in terms of ideological consistency, he’s an old school hawk on national security, and he likes the spying and counter-terror laws just as they are.

Now, these two are on a collision course for Sunday evening’s session, when – after Paul’s repeated objections to any extension of the law last weekend – the Senate faces an 8 p.m. deadline on what to do, or else the laws will expire however briefly.

FIX: So, the arc you lay out suggests the ultimate marriage of convenience. Paul beat McConnell’s guy. That made McConnell worry about his own hide.  He buddied up to Paul. Paul reciprocated because he wanted some of the establishment/mainstream cred that oozes off of McConnell as he considered running for president. But now, McConnell and Paul have very different interests; one is trying to prove his party can run Washington, the other is running on the idea that Washington Republicans are a big part of the problem.

Which leads me to this: Were McConnell and Rand ever really friends (or even friendly)? Or was this your classic use-use political relationship. I guess what I am getting at is whether McConnell is bothered (or surprised) by what Paul did on spying last week. Is there any sense of betrayal? Double-dealing?  

Or, do McConnell and Rand both see each other for what the other is: One a backroom wheeler-dealer, the other a shake-up-the-system philosopher?

PK:  I know people hate this kind of wishy-washy answer, but I think it’s probably a little bit of both. They were probably never as far apart as we assumed they were, and they were never as close as we made them out to be.

McConnell is a quintessential political being, who has the deepest respect and admiration for people with good political skills and instincts. I do think that McConnell admired Paul for that skill set. Yes, his father was a congressman, but an oddball one who wasn’t skilled enough to win anything more than a House district. McConnell liked Rand’s political capabilities, as a candidate. He probably questions his capabilities to run an actual national campaign, which is a much bigger leap than winning a primary.

Paul liked learning how to build insider coalitions from McConnell, who is a master at that kind of stuff. He wanted more than just to offer up amendments that only got five votes in support, and being close to McConnell helped in that regard.

Directly to your question, however, no, they were never very friendly. Generationally cut from a different cloth, their pursuits are very different. Paul had his eye on the White House from the moment he took the oath, and McConnell never aspired to anything more than his current post. McConnell lives in a townhouse about half a block from the Hart Senate Office Building; Paul lives in a mile or so away, in a high-rise apartment complex with a roof deck that on weekends is crowded with 20-somethings hosting parties.

They don’t really socialize, but they appreciate each other’s strengths, respect each other’s strong suits and are happy to work together when it fits both their causes.

Pause for Denny Hastert revelations and the death of Beau Biden. Pick up Monday morning.

FIX: It feels like this whole thing jumped up a notch -- to paraphrase and "Anchorman" quote on Sunday night. 

McConnell, with Rand sitting there on the floor listening, blasted the "campaign of demagoguery and disinformation” around the Patriot Act.  He seemed genuinely peeved.  

Am I wrong? And, if I’m not, what does this mean for their relationship going forward? I mean, McConnell has endorsed Rand’s presidential bid, right? How does he look if one of the main pillars of that bid is a policy on the NSA that McConnell quite clearly disagrees with?

Second point: It’s clear that the majority of the Senate — especially on the Republican side — is back to hating Paul after a period of détente. John McCain said again on Sunday that Paul would be the “worst” possible presidential nominee for their side. What, if anything, can senators like McCain do to hurt Paul?

PK:  Oh yeah, it most definitely did jump another notch up. I don’t think anyone killed anyone with a trident, like in the Anchorman fight scene, but it’s gotten nastier.

Just now, Monday afternoon, McConnell went to the floor and demanded that the next set of votes get moved to 6 p.m. and a final vote Monday night. “We all know how this is going to end,” he said, almost yelling, something he usually reserves just for when he’s mad at Harry Reid’s parliamentary tactics.

And standing there a few rows behind McConnell was Paul, to object, and say that he’d only give in if the GOP leaders gave him a few amendment votes of his own. They won’t. So he objected, and the debate drags on another couple days.

McCain’s goal, politically, is to wound Paul on foreign policy matters. While he is not beloved by conservatives because of his wheeling-dealing ways with the likes of Ted Kennedy, McCain still has bona fides on foreign policy among conservatives. And his increasingly sharp attacks on Paul are designed to weaken him in early voting states among the increasingly large group of Republicans who view national security to be their most important issue.

Even though he’s not on stage in debates, McCain’s views will work their way into the questions Paul faces, from Iowa to New Hampshire (where McCain remains very popular, having won that state’s primary in 2000 and 2008).

FIX: OK, last thing: Who “wins” here: McConnell or Rand?  Or are they playing different-enough games that declaring a winner and a loser doesn’t work?

PKI’m going to do the opposite of what we so often do in political reporting (declaring them both winners), and I think they’re both losing in the short run.

Paul’s positions seem to be out of step with many traditional conservative voters, and while it’s admirable for him to maintain his ideological consistency, I think it will put a ceiling on his ability to reach primary voters because they might like him on a many positions but will be fearful of putting him in control of the military.

The NBC/WSJ poll found early last month that national security/terrorism is now the No. 1 issue for Republican voters, and most of those voters are traditional hawks more in line with McCain.

And McConnell, while he will ultimately get most of the anti-terror laws restarted, it will have come at some institutional cost. He got briefly outmaneuvered by a junior colleague with barely four years experience, on an issue of utmost concern to McConnell, with a hand of cards that was clear to him several weeks out.

He went with the old playbook of relying on the smell of jet fumes and a week-long recess over Memorial Day, just tire out the rank-and-file and they’ll eventually say “uncle”and you’ll get your way – the old playbook doesn’t work that way all the time now. It’s changed.

Seeing McConnell get outmaneuvered around like this, reacting to others rather than setting the play and executing, was shocking to see. Almost as shocking as that time an eye doctor from Bowling Green, five years ago, defeated McConnell’s choice in a Kentucky primary.