As Kamala Harris' campaign shows signs of stalling, some are questioning if her choice of running mate, far-left Minnesota governor Tim Walz, could cost her the race.

When Harris plucked Walz out of obscurity weeks ago, many were surprised she did not choose Pennsylvania's popular governor, Josh Shapiro.

Of all the battleground states, Pennsylvania is the most crucial. But the race is tightening there, in a worrisome sign for Harris and her path to victory.

Did Harris mess up?

There were rumors when Harris snubbed Shapiro that she was put off by his personal ambition, while others pointed to left-wing anti-Semitism toward the Jewish Democrat.

Whatever the reason, the Harris-Walz ticket is losing momentum. Harris is now tied with Donald Trump in Pennsylvania, CNN's Harry Enten pointed out.

Shapiro has a 59% approval rating in the state, Enten noted.

"What we saw was a small Harris lead, but within the margin of error, becoming a race that is way, way, way too close to call at this particular point. One that is even," Enten said.

"The bottom line is if Kamala Harris loses in the state of Pennsylvania...there are going to be some real questions as to whether Kamala Harris should have chosen Josh Shapiro given how popular he is in the commonwealth of Pennsylvania," Enten said.

"Could she have been a winner if she had chosen him instead of Tim Walz?"

Missed opportunity

A sobering New York Times/Siena College poll released Sunday has Trump beating Harris by one point nationally. The poll also shows that voters see Trump as more moderate than Harris, who was rated "too liberal" by 47% of likely voters.

Pollster Nate Silver, whose forecast pegs Trump's odds of an Electoral College victory at upwards of 60%, said Haris missed a "big opportunity" to appeal to moderate voters by choosing Walz, an unabashed leftist.

Harris' campaign has retracted many of her past radical positions, but Harris has struggled to explain her shift to the center in her own words.

Of course, if Harris loses, it will probably be because of her own shortcomings and not because of who she chose for a running mate. She took a big risk by avoiding the press for weeks and failing to answer tough questions about policy.

If she falters in Tuesday night's ABC News debate, she will have nobody to blame but herself.