I have an old friend for over 50 years. He was always religious, but generally rational and intelligent. In his old age, he has become so obsessed with religion, bombarding me with preposterous religious ideology and predictions and constantly trying to convert me. At the same time he turned to the extreme political right.

We had been communicating several times a week for many years, but it got so bad I had to tell him that I will not discuss religion, politics, or economics with him. He finally got the message when I did not respond to his continued attempts. How, we communicate only 3 -4 times a year, on nothing of substance.

It really sucked when you are in a romantic relationship and your partner finds god. It’s like they started believing in Santa. You want to call them on it, but just like children, it will be a problem to tell them the truth!

I got dragged to a church a number of years ago. Across the room I spotted an old friend. I figured he got dragged there as well. Once I started talking to him I quickly realized “they got him. He had found god”. The rest of my evening sucked!

Becoming born again as an adult is largely an emotions-based process, relying on low self esteem, vulnerability possibly caused by trauma, dependence on authority, the need to belong, among other things. It's very closely related to cult mentality and group-think. I feel for you, and admire the fact you're not just shrugging your shoulders and writing him off. Most people (including relatives) did that with me, which only strengthened my resolve that I was right.

Stay his friend as long as he will let you - You may be his only anchor in reality. If he's seeking truth, he won't find it in his current path.

oh yeah, it happens relatively frequently...especially with people who have vices they need to be rid of....I like to 'mine someones belief system', in that I like to question their ideology, and have them question mine...but you can't do that very well with 'fresh cuts'...people newer to their religion, they get offended easier....the doubts are closer to the surface, so they have to defend it with obstinence....but it is better to just let them have their belief then tempt them back to the vices that were probably killing them....your situation sounds like somebody was having a crisis or crises, and chose to deal with it through outside tenets...avoid the subject would be my suggestion...but the worst is if they are all 'converty'....then you get that antagonistic relationship that you are happy to see end...wait....that may be the win...haha

Yes, a childhood friend in adulthood turned to the dark side. It appeared to have happened through marriage and fatherhood. Always extreme, it seemed that in order to change his lifestyle and atone for his many ‘sins,’ he needed a god... He did have a lot to answer for! ...as I know where many of the skeletons are buried..

We’ve had some deep talks, and he knows ‘I get it,’ but to find he couldn’t live a responsible life without the parameters of religion confirms that we were more friends by proximity than shared understanding... He’s now a hardcore greedy republican attempting to buy his way to ‘heaven.’

Possibly the biggest problem is that anyone opposing a persons faith is labelled as the devil tempting a person.

And when salvation is based on believing then the victim is blackmailed into continuing to hold course.

So reason is blocked both against intrusion and against self doubt.

Might be good to explain this to him.

And at some time later ask if the Genesis Flood was local or global.

Christianity is big on promise and small to nonexistent on delivery

The only reason there is a significant number of Christians is the existence of successful delaying tactics.

The promise that anyone who is in Christ is a new creation is the big promise. The only reason everyone doesn't wake up the next morning and say 'well that didn't happen' is due to the delaying tactics of which there are several.

Delaying tactic 1
The booklet explains that some people (some?) feel no different but that
like when you were born the first time you need time to grow
Delaying tactic 2
you also need, like food and air and exercise read the bible, pray and evangelise every day and then you will grow, and it will be slow but you can trust god who never lies that the seed planted within you is growing.

Most people after a number of years realise nothing has happened and the promise was hollow.
Delaying tactic 3
But there are further promises about what will happen after death and there is the lost cost fallacy to entrap people into 'remaining faithful to the end'.

I've lost many friends to RELIGION or drugs...not sure which was worse

Yep a lovely guy when at college I went to see him and his wife .. they had two children. I was pregnant with my first child and was proudly showing off my partner... he took me aside and said we would have to sleep in separate rooms because he didn't want his children to think sex outside of marriage was acceptable. Haha I knew him pre born again and he certainly slept with a number of fellow students lol needless to say we didn't stay long

his mum must be in terrible pain

Yes, unfortunately. Not best friend, but a close friend. Things start off amicably enough, but every time we met I was just waiting for the moment when god would enter the conversation and that sometimes ended up being heated. We rarely speak these days; I just couldn't handle having to listen to illogical arguments over and over. Seems you're going through a similar experience.