No wonder John Mara was outraged at the suggestion he is ruling the Giants with sentimentality.

This goes back much further than Giants icon Eli Manning and his scrutinized final seasons. The franchise’s co-owner and chief decision-maker decided decades ago not to make the same personnel mistake as his father.

So when Mara’s voice raised a few decibels, his face became flushed and his hands fidgeted last week when asked about sticking with the 38-year-old Manning as quarterback, it was because he is being accused of breaking a vow made to fans.

In August 2000, when it was clear John eventually was going to succeed his father Wellington atop the organization, John granted The Star-Ledger a forward-looking interview. The words he said never have been more relevant than right now.

The Giants had just forced into retirement center Brian Williams, an 11-year veteran nowhere near the stature of Manning.

Wellington pleaded with Williams, who even admitted to being washed up, to return for one more season rather than call it quits. But the Giants, led by John, offered a minimum salary and with it the prospect of being cut in training camp.

“In the past, my father would have made him a coach or offered him a front-office job,” John said at the time. “He was too loyal to people who had been with the organization and made great contributions. But they weren’t always the best qualified to be in leadership roles. It took us decades to recover from that.”

After winning a fourth NFL championship in 1956 and reaching the championship game but losing five times in a six-year span from 1958-63, the Giants discovered misery. There were two winning seasons and no playoff games from 1964-78.

There are no banners hanging from planes flying above the Meadowlands, but the Giants are in the dark days again.

Is it just the beginning? The middle? Are they almost over?

“Loyalty is a wonderful trait, but you have to know when to be loyal and when to do what’s best for the organization," Mara said in 2000. "I don’t ever want to go back to those days. They were painful decades.”

Since winning Super Bowl XLVI in February 2012, the Giants have one playoff appearance (and no wins) in seven seasons.

They are tied with the Browns with a NFL-high 24 losses in the last two seasons combined, but the Browns are trending upward thanks largely to drafting the right young quarterback (Baker Mayfield) when the Giants passed on a similar opportunity and to a trade with the Giants for mercurial wide receiver Odell Beckham.

The outraged John called keeping Manning a “football decision” and said it “really gets under my skin” to read the Giants are keeping their two-time Super Bowl MVP as the starer because of sentimentality.

“That is absolutely nonsense," John said last week. "Do I feel a certain amount of sentimentality towards Eli? Of course I do. Would I ever let that get in the way of making a football decision? Absolutely not!

“I would never tell the coach or general manager, ‘We have to keep this guy because we love him and because he’s done so much for the franchise.'

"Make a football decision based on whether you think he can play or not. If you think he can, if you have a conviction and the coach has a conviction, that’s fine. I’m never going to interfere with that based on my sentiment towards a player.”

Another lost season in 2019 — the final year of Manning’s contract — might force John to prove it in a tough spot. Already asked about a contract extension for Manning, John said the plan is to take it “one year at a time.”

“He will make a wonderful owner,” Wellington said of his son to The Star-Ledger in 2000, five years before his death. “When it comes to letting a player or coach go, sometimes I struggle. But John can see past the sentimental.

"Because he was raised with the Giants, he has a wonderful sense of the history of our family and this team, and he loves it as much as any of us. That’s what guides him.”

Ryan Dunleavy may be reached at rdunleavy@njadvancemedia.com. Follow him on Twitter @rydunleavy. Find our Giants coverage on Facebook.