Monday night, the Passtronaut turned into a space cadet, and the improbably buoyant Vikings fell to Earth.

Joshua Dobbs, former aerospace engineering student, became one of the best stories in the NFL for a reason.

That reason: Improbability.

There was little logic in the story of a career backup who had made eight previous stops in the NFL, with seven different teams, becoming the Vikings' imported midseason savior.

Monday night, Dobbs' story was introduced to the laws of NFL gravity. In his fourth game for the Vikings, he threw four interceptions, leading to a second consecutive loss and a major blow to the Vikings' postseason hopes.

His fourth-quarter touchdown pass to T.J. Hockenson gave the Vikings a one-point lead that was erased by Cairo Santos' 30-yard field goal with 10 seconds remaining, giving the otherwise woeful Bears a 12-10 victory, their fourth of the season.

You could say the loss was costly, because Kirk Cousins and Justin Jefferson may have become much more expensive on Monday night.

NFL backups can give you a good game, maybe even a good month, but it is rare that they can replace a star-caliber player for any length of time once opposing defensive coordinators have identified their weaknesses and tendencies.

That's why star quarterbacks (and perhaps a certain receiver) can command half-a-billion-dollar contracts, and most backup quarterbacks bounce from team to team until they become coaches or accountants.

The Bears were well aware of Dobbs' tendencies on Monday, making him look more like the quarterback who couldn't hold a job than the magician who won his first two games after being traded to the Vikings.

Dobbs completed 22 of 32 passes for 185 yards and a touchdown, but those numbers obscure reality.

The four interceptions and the Vikings' slow start offensively offset any passable final statistics.

When a quarterback plays the way Dobbs did on Monday, the fan base is likely to call for him to be replaced. The Vikings' alternatives are longtime NFL backup Nick Mullens and 2023 fifth-round draft pick Jaren Hall, who looked competent while completing eight of 10 passes against Atlanta before suffering a concussion and being replaced by Dobbs.

Asked if he would consider a quarterback change, Vikings coach Kevin O'Connell said, "We'll take a look at everything,'' and mentioned that Hall and Mullens are healthy. "We did not have the performance we wanted offensively," O'Connell said.

The Vikings, now 6-6, have a bye this weekend, followed by what should be a winnable game at Las Vegas.

O'Connell will have to weigh Dobbs' erratic play on Monday against Hall's inexperience. At this moment, I'd opt for Hall, if he's completely healthy.

Dobbs had to scare O'Connell with his first-half performance.

In the first quarter, the Vikings produced minus-7 yards. According to ESPN Stats & Info, that was the fewest in a first quarter since Week 1 of 2019, when the Bears held the Packers to minus-12.

The Vikings' first three possessions produced two interceptions and a three-and-out.

They didn't score until the last play of the half, on Greg Joseph's 34-yard field goal.

Hockenson, who was the last player introduced during the pregame festivities, didn't have a first-half reception.

Midway through the fourth quarter, receiver Jordan Addison ran open down the left sideline. Had Dobbs thrown the ball inbounds, Addison likely would have scored a go-ahead touchdown. Instead, Dobbs led him out of bounds.

Dobbs again displayed his mobility, especially while escaping pressure in the pocket, but the Bears seemed eager to take advantage of his mediocre arm strength. He was lucky that at least one first-half pass wasn't intercepted and returned for a touchdown.

This kind of play can't be tolerated, much less rewarded, and the Vikings no longer have any margin for error.

They are a half-game ahead of the Packers (5-6), and closer to the last-place Bears (4-8) than the first-place Lions (8-3) in the NFC Central.

Jefferson's return should help their cause, but only if they have a quarterback who can get him the ball well downfield.

Dobbs gave the Vikings more than they could have expected. His creative play, combined with his charisma and intelligence, made him one of the best surprises of the NFL season.

Until Monday, when he stopped defying gravity.