We’re halfway home at the 117th U.S. Open, the first of its kind in the American midwest, and all that we know is what we don’t know. We don’t know why certain names have played the enviable shots they’ve managed, and we don’t understand how others were incapable of the same execution… and have checked out of their hotels.

The story is half told, and the climax yet awaits. For now, let’s focus on 5 things we learned from Day 2 of the 2017 U.S. Open.

1. Paul Casey, Super Chill

This 3-iron laser sets up a birdie and share of the #USOpen lead for @Paul_Casey. https://t.co/tLvfaywUsT

— U.S. Open (USGA) (@usopengolf) June 16, 2017

If someone intimated that a contender would play a four-hole stretch in bogey-par-triple bogey-bogey, dropping five strokes to par, and still be tied for the lead at day’s end, you’d certainly consider him daft. And yet, that’s the story of Paul Casey, late bloomer.

Casey nearly matched Adam Hadwin’s six-birdie run with five of his own, but we’ll get to that in a bit. After birdie on his second hole of the day, the wretched stretch followed, and Casey stood 4-over par on the day, 2-under over the long haul. As mentioned yesterday with Sergio Garcia, those with great patience exhibit it at the most appropriate moment. Casey calmly made par on No. 7, and then he ran the table with a quintet of birdies.

With six pars to close his back nine, Casey joined Brian Harman, Tommy Fleetwood, and Brooks Koepka at 7-under, one shot clear of Jamie Lovemark. After a mid-career crisis in the late 2000s, Casey has rediscovered his massive talent and appears poised to claim a spot in the pantheon of Tiger-era major champions.

2. Happy Birthday, Champ!

And around we go!

Amateur @CameronChamp54 finishes 36 holes at 5 under. #USOpen https://t.co/e35xrVy9kF

— U.S. Open (USGA) (@usopengolf) June 16, 2017

Cameron Champ celebrated his birthday on Thursday with a 2-under 70. It was his first major championship, and the rising senior at Texas A&M impressed the golfers with his game — and the muscle crowd with his prodigious length off the tee. Friday came and went, and Champ is not only still around for the weekend, but he’s inside the top-10 after 36 holes.

Champ had five birdies and two bogeys over the course of his second go-round at Erin Hills. Although he hit fewer fairways and greens in Round 2, he played the pro game and scrambled his way to an even better score. If he hasn’t celebrated his special day yet, he has some time tonight thanks to an afternoon tee time on Saturday.

3. On, Wisconsin!

You think @SteveStricker wants to play the weekend in front of his home crowd? #USOpen https://t.co/a0rRfbae8X

— U.S. Open (USGA) (@usopengolf) June 16, 2017

Odds are that favorite sons of Wisconsin Steve Stricker and Jordan Niebrugge will not return from 1-over after 36 holes to claim the 2017 U.S. Open trophy. The fact that both fellows passed the halfway test and will be around for the weekend is a heart-warming story line, perhaps found only here in “5 Things We Learned.”

Niebrugge was an unexpected member of the 2013 U.S. Walker Cup side, and he returned to the team in 2015. Since then, he has endured the grind of the young professional. Two late birdies on Friday (Nos. 16 and 17) brought the Mequon native inside the cut line.

Stricker, the wizened Tour winner, was not accorded the exemption that many felt he deserved; he earned his spot in the field over 36 holes in early June. Unlike his younger counterpart, the PGA Tour veteran was well inside the cut line until two bogeys on his inward half made things dicey. Fortunately for Edgerton and Madison, Stricker parred out and on he plays.

4. The Major Lurkers Club Has Convened at Erin Hills

A 7-under 65 in Round 2 helped Hideki Matsuyama erase a 2-over 74 from Round 1 and earned him Friday's @Lexus Performance of the Day. pic.twitter.com/5JlrbXkyE1

— U.S. Open (USGA) (@usopengolf) June 17, 2017

These fellows own not one major professional title, but their names make the headlines during nearly every playing. Charley Hoffman, J.B. Holmes, Marc Leishman are among them. These are professional golfers with success at every level of the game. From national squads to amateur and collegiate (and even Tour) triumphs, they have earned every recognition save one: major champion.

What will it take for Hideki Matsuyama, Bill Haas, Bernd Wiesberger and others to enter the ranks of major championship winners? That recipe has no script. It might be a critical par save on Thursday, a long birdie putt on Friday, a fortuitous pairing on Saturday, or a gut-wrenching final nine holes on Sunday. These and others will figure this weekend, but will they win? Stay tuned.

5. What To Do, What To Do, in Wisconsin This Weekend?

Way to finish your round ???? @Knohles. #USOpen https://t.co/88Qfpbb3HT

— U.S. Open (USGA) (@usopengolf) June 16, 2017

We bid farewell to a number of pre-tournament favorites (Justin Rose, Jon Rahm, Rory McIlroy, Adam Scott) and recent major champions (Henrik Stenson, Dustin Johnson, Jason Day) as the cut falls at 1-over. On a golf course with linksy, dunesy, parksy qualities and characteristics, what might be the culprit? Who knows!

The same twists of fate that allowed Xander Schauffele to shoot 66-73 and stand inside the top-10; Chez Reavie to fire a 65 on Day 2, a full 10 strokes lower than his Thursday effort; and Tyler Light to birdie three of his final seven holes (and bogey two others) and sneak inside the top-68, conspired to send the aforementioned luminaries away.

As they say, rub o’ the green.