Here’s the case, put relatively well:
Moral superiority aside, a somewhat general rule of thumb is that if you have children AND they live in the same country, then you have a HIGHER vested interest in the wellbeing of your country.
I’ll take “wellbeing of your country” to mean wellbeing of the residents of your country, though it doesn’t have to mean that.
Now, this argument is one that’s true sometimes. But only sometimes. It also assumes that parents care about the wellbeing of their children, which isn’t always true, but we’ll assume it is for now.
Let’s run thru why it doesn’t work for powerful people, which includes most politicians, certainly anyone with a decent chance of winding up President of the United States.
It is possible to take actions which increase the wellbeing of your children, which also harm the wellbeing of your country. American politicians and oligarchs, for example, sold America’s manufacturing base to China. They become filthy rich as a result and their children will be very well taken care of even if America is in serious decline. It did, however, harm the majority of Americans. (There are thousands of other examples, feel free to add some in comments.)
Your children may live in a worse-off America, but they are better off than if you did not do that harm. (Or, at least, that is your belief.)
If you prioritize the wellbeing of a small group over a larger group it usually possible to hurt the larger group to benefit the smaller group.
In fact, there is a strong argument that people without children are far more likely to prioritize the wellbeing of the residents of their country than those with children: they don’t have to make a choice: “should I make my kids better off OR the everyone else better off?”
Even at the simplest level, of “should I spend more time with my kids OR spend more time doing my job” there is this conflict. Great men and women are often bad parents, because if working an extra hour means helping a thousand of someone else’s children, they do that even if it hurts their own kids.
There is no free lunch. You always have to prioritize.
Harris will be a terrible President, I’m confident of that. But it has nothing to do with whether or not she has kids and, in fact, if she intended to do the right things for ordinary Americans, the fact that she didn’t have children would be a significant plus.
Most cultures have a family worship disease: the idea that you should always put your family first.
NO.
If you are willing to put your family first when doing so means that large numbers of people will suffer, you’re a monster. In fact, one of the necessities of having power over large numbers of people has to be that you don’t put your family first IF doing so will result in harm to others.
If you reach a point where it’s your family or a large number of others, and you can’t choose the “others” then you should step down and give the job to someone who can take care of the others.
Only those without power can, ethically, prioritize their own family without being monsters.
That this has to be explained to people is another sign of our inability to reason clearly about moral and ethical issues.
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If I were an American, I’d be pretty happy about the guy, unless I have a problem with mass murder of foreigners.
So, an attempted Presidential assassination, and now Biden has 
I’ve been saying it mattered a lot for quite some time, but, 
The debate made it clear that Biden is in serious decline. Remember that it’s not just about now, it’s about four years from now. The media has turned on him hard, and so have many in the Democratic party.