Political pledges often cause headaches. On election night in 1904, President Theodore Roosevelt told reporters, "Under no circumstances will I be a candidate for or accept another nomination." He regretted it almost immediately. Later, he would say, "I would be willing to cut off my hand if I could call back that statement."

In 1988, accepting the Republican nomination for the presidency, George H. W. Bush pledged "no new taxes." Bush did wind up agreeing to raise taxes. It may have been the right governing choice, but because he had pledged in such memorable terms not to do it, he stirred a profound sense of betrayal among Republicans and encouraged cynicism about politicians in general.

On March 15, Joe Biden pledged to choose a woman as his running mate. Now, that pledge is weighing him down. He has delayed the announcement of his choice by a week, suggesting that it is proving more difficult than expected.

It's great to pick a woman for vice president, but less great if you've first pledged to do so. The pledge telegraphs that you were not looking for the best person, but the best woman. Biden could not know in March that the country would be convulsed by the death of George Floyd at the end of May and that pressure would build among Democrats for the ticket to include an African American. Absent that pledge, he could be considering Sen. Cory Booker, D-N.J., or former Gov. Deval Patrick of Massachusetts.

Few Black women have the experience and stature to step into the presidency.

Don't get me wrong. The paucity of African American women in top-tier political roles is the result of centuries of slavery and discrimination. But it is a fact nonetheless. There is only one African American woman United States senator. There are no governors.

Any presidential candidate, and particularly one who will be 78 on inauguration day, needs to choose someone ready to step into the job at a moment's notice. That someone needs to have governing experience. She needs to have endured the pitiless spotlight of national politics. She needs to be broadly acceptable to swing voters. And she needs to be someone the president trusts completely.

Among the women who meet the above tests, there are problems. Sen. Kamala Harris has been exposed to the scrutiny a campaign brings, but she forfeited some trust with Biden by aiming an insulting charge at him, suggesting that he allied with racists on busing decades ago.

Susan Rice has a distinguished record of public service but has never run for anything. She is also, potentially, quite a lightning rod. She misled the country about what had happened in Benghazi, Libya, in 2012, and Trump partisans believe she was part of a conspiracy to damage the incoming Trump administration. The latter accusation against her is mostly rubbish but could cause a needless sideshow in the fall.

Rep. Karen Bass heads the Congressional Black Caucus. People like and respect her, even Republicans. But some troubling statements and associations have surfaced. In 2010, she spoke at the opening of a huge Scientology Center in Los Angeles. Questioned about this, she tweeted last weekend that she had appeared there because the center was in her district -- which isn't much of an explanation. But that wasn't even true. She tweeted on Aug. 5 that she "regrets the error."

Bass eulogized Oneil Marion Cannon as a "friend and mentor" in 2017 without mentioning that he was a long-time member of the Communist Party USA. As a young adult, she was a member of the Venceremos ("we shall triumph") Brigade, a pro-Castro group, and traveled to Cuba eight times in the 1970s. When Castro died, Bass released a statement of condolences to the Castro family and the Cuban people: "The passing of the Comandante en Jefe is a great loss to the people of Cuba."

Look, Donald Trump has said equally appalling things about Kim Jong Un. The Republican Party that stands with Trump is hardly in a position to throw stones at Bass.

And yet, we are told that part of what made Trump possible was the tendency on the right to look the other way about the extremists, kooks and unsavory elements within their own ranks. The same rule should apply to Democrats. Besides, choosing such a confirmed leftist would alarm the centrist voters Biden will need.

Time for a closer look at Senator Tammy Duckworth, D-Ill., and Rep. Val Demings. Duckworth's likability and story of heroism and sacrifice are powerful. Val Demings is a former police chief. The disadvantage is that there is no police department in which stories of wrongdoing will not surface. But the upsides are greater. Who better than an African American former cop to address questions of police brutality with sensitivity? And who can accuse the Democrats of being the party of "Defund the Police" with Val Demings on the ticket?

Biden is about to become the Democratic nominee because he was perceived to be safe. He should choose someone just as safe for VP.