Early last year a high-level official who helped Beto O’Rourke weigh whether to get into the presidential election examined the field and came up with the following conclusion: “If all Beto has to do is get by Joe Biden and Bernie Sanders, I like his chances.”

At the time O’Rourke, the former congressman from El Paso, was running third in the national polls, behind Biden and Sanders.

You know what happened. O’Rourke got into the race and flamed out before the Iowa caucuses. He’s not alone. Many of the 25 or so candidates that were running for president have vanished from the scene, including Sens. Cory Booker of New Jersey, Kamala Harris of California and Kirsten Gillibrand of New York.

What’s clear now, and should have been obvious then, is that Biden is the most formidable candidate in the once large field. His connection with the Democratic Party’s most reliable voters is unshaken by months of presidential debates, as well as media and political pundits predicting a Biden collapse.

The former vice president is far from a paper champion, as his rivals are beginning to realize. Yes, the voting hasn’t started yet and he can still be knocked off course. A poor finish in Iowa could start a decline, though Biden has dramatically improved his standing in that caucus state.

It’s Biden’s race to win or lose. Here’s why.

As many candidates rushed to embrace the progressive policies outlined by Sanders in the 2016 presidential primary, Biden stayed close to the middle. He’s assuring voters that on the health care issue, abolishing private insurance doesn’t make sense. That’s probably where most voters are on that issue as well.

In taking a more moderate tone, Biden bolstered the notion that he’s the best chance to oust President Donald Trump in November. With nicknames like Scranton Joe or Middle-class Joe, Democrats hope Biden can return states like Wisconsin, Michigan and Pennsylvania to the blue column.

Whether the other top contenders can restore the Midwestern wall Democrats once enjoyed is an open question.

Biden also benefits from being familiar to voters. As vice president under Barack Obama, he enjoys strong support with middle-aged to older black voters, the most reliable cog of the Democratic Party. No other candidate in the field approaches his popularity with black voters, which will be important when the presidential race leaves Iowa and New Hampshire.

Attempts by Harris and former San Antonio mayor and former Housing Secretary Julián Castro to attack Biden during presidential debates had only short-term gain and ultimately backfired. Biden has seemingly stumbled at some debates, but that hasn’t impacted his standing in the polls.

There is something to be said for a fresh, more energetic candidate. That’s been the appeal of former South Bend Mayor Pete Buttigieg and was supposed to be a positive for O’Rourke.

But the overwhelming desire to beat Trump has many voters settling on the tried and true.

Even though he’s the clear frontrunner, Biden has to guard against complacency or taking a lead for granted. He tops most of the polls for the March 3 Texas primary and has most of the major endorsements. But his field operation lags in comparison to his rivals -- he’s yet to open an office here - and it appears most of his ground work will take place after the Iowa caucuses. Texas is a large, complex state and being organized here is important.

Still, Biden is in the driver’s seat. After being underestimated for most of the summer, Biden is proving that experience, connections and a simple message can still go long way, maybe to the nomination for president.