As far as the USA is concerned, no conviction is ever 'spent' because the USA doesn't recognise the UK's Rehabilitation of Offenders Act.
The USA has no
direct access to UK criminal records at the moment because EU law prohibits the UK from making them available to the USA. However that's likely to change after Brexit, as the USA is known to require direct access to a country's criminal records as part of any trade deal that it might enter into with such a country.
However the UK does make such information available to the USA upon receipt of a specific request for such information. (There seems to be some evidence that the USA makes far more such requests than are actually required to prevent terrorism, so it's not clear what criteria they use when deciding whether or not to seek the information).
I've been reading (and responding to) many questions like yours for well over a decade on this site. There have been plenty of people who've stated that they've managed to get into the USA by 'forgetting' criminal convictions when applying for an ESTA. However there have also been just a handful from people who've been refused entry.
You also need to consider what might happen if you can't get into the USA. Up until recently, trying to enter the USA without valid documentation wasn't a criminal offence in itself. All that could happen was that you'd be held in confinement until you could be placed on a flight back home. (Even then, that could be problematic as, in addition to losing out on your holiday, you'd have to pay for a flight ticket purchased at 'on the day' rates, the price of which could run into thousands of pounds). However the Trump administration has now made it a criminal offence to seek entry into the USA without the correct paperwork, meaning that you can now be imprisoned for doing so.
As I've already said, lots of people do currently manage to get into the USA by failing to declare their criminal convictions but there's always going to be a risk (and, with the UK leaving the EU, that risk might get substantially greater). It would be far safer to seek a visa.
Harassment doesn't count as a crime 'of moral turpitude' unless it was racially aggravated. (Source:
https://hub.unlock.org.uk/knowledgebase/identifying-whether-my-offence-is-a-crime-involving-moral-turpitude-cimt/ ). So, assuming that there wasn't any racial element involved, you'd only need to convince the US Embassy that you should have a visa (rather than to seek a 'waiver of inadmissibility' from Washington, as you would need to do for a crime involving 'moral turpitude').