The Vikings head into two bye week practices as the winners of four straight, behind a quarterback who has directed all but six quarters of their 6-2 start.

At the halfway point of the 2017 NFL season, Case Keenum ranks 12th in the NFL in completion percentage. His passer rating of 88.8 puts him 16th in the league, just between Matthew Stafford and Philip Rivers. By ESPN’s Total QBR metric, Keenum has been the seventh-best passer in the league this season, a shade more effective than Aaron Rodgers, Russell Wilson and Matt Ryan.

Why in the world, one might ask, would the Vikings think about making a change? Because behind Door No. 1 might be the quarterback on whom they’d staked their franchise only three years ago.

The Vikings have until Nov. 8 to make a decision about whether to activate Teddy Bridgewater from the physically-unable-to-perform list and return him to their active roster for the second half of the season. All indications are Bridgewater continues to make solid progress in his return from the left knee injury he suffered in August 2016, and it’s a real possibility the Vikings could have him back on the field as soon as a week from Sunday against the Redskins.

(It’s at this point we pause for the requisite word of caution: Bridgewater hasn’t taken a hit in a game since his catastrophic knee injury. His last game snaps were on Aug. 28, 2016, when Norv Turner was still the offensive coordinator, Adrian Peterson was slated to be the featured back and Adam Thielen hadn’t yet emerged as the team’s top target. And just 14 months ago, Bridge-water’s prognosis was so dire it seemed he might never play again.)

Consider all that Keenum has done, all that remains unknown with Bridgewater, and then realize this: On Sunday, coach Mike Zimmer sounded entirely willing to consider the possibility of a quarterback change.

“Hopefully, I have a decision to make,” Zimmer said, when a reporter suggested he had an upcoming decision at QB. “I don’t know any of that yet. I don’t know. We’ve got two days of practice next week, got another day of practice on Monday. We’ll sit down, evaluate everything. Case has done an unbelievable job. He’s done what we have asked him to do, he’s come out and kept things rolling, and we’ll just figure it out as we go. We’ll see. I hope I have to make a decision.”

If the Vikings did return Keenum to the No. 2 quarterback role on a first-place team, it might be because they’re concerned whether his ceiling is high enough to keep them winning during a second-half schedule that begins with five games — four of them on the road — against teams with a combined 20-16 record.

Keenum is 13-17 in his career as a starter; he’s matched a career high with four wins this season. His career completion percentage is 59.7, and his passer rating is 80.8. Bridgewater put up modest numbers in his first two years as a starter, but the Vikings believed he was ready to make a significant leap in Year 3 before his knee injury. If they decided to make a switch, it might be motivated by a quest for more upside.

In his past two games, Keenum has endured rocky starts before rebounding in the second half. He’s thrown interceptions on the Vikings’ opening drives each of the past two weeks, and misfired on several early throws in both games. He went 30-for-49 in the first halves of those games before going a combined 17-of-25 for 194 yards and a touchdown in the second half against the Ravens and Browns.

“I thought early it was a little spotty, but in the second half, I thought he made some great throws,” Zimmer said on Sunday. “He took care of the football. I thought he played great in the second half.”

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If the Vikings were to add Bridgewater to the 53-man roster, there’s no mandate they make him the starter immediately. They theoretically could let the situation play out as long as they like, and a healthy Bridgewater, at the very least would give them another proven quarterback with no end to Sam Bradford’s knee issues in sight.

“For me, I just take it a week at a time,” Keenum said Sunday. “As a kid growing up, I mean, I couldn’t have even imagined getting to come to London to play a NFL football game. Like, that’s a dream come true as a kid. So to come over here, to see the sights, to play in front of a really cool crowd in an incredible rugby stadium, it’s a blast. So I don’t think too much about the big picture of things, I take it a week at a time, and I’m loving what I’m doing.”

However things play out, the Vikings could return from the bye with four quarterbacks on their roster, three of them (Bradford, Bridgewater and Keenum) potentially hitting free agency after the season, two of them former first-round picks and only one able to play at a time.

The countdown to their QB decision appears to be on.