The Guardian with lengthy piece, and video, marking 30th anniversary of Born in the USA, on how Springsteen "became political" at that time, partly thanks to Ronald Reagan (and George Will?). As early friend and writer about Bruce (circa 1972) I can vouch for his "lack of politics" back then, and for years, and yet it did develop just before release of that album. Steve Van Zandt certainly played a role. But as for activism, his thing on big tour after that album came out was meeting with vets, going to their offices and hospitals and holding fundraising concerts for them (or outright just giving money), and for food banks and other community help groups. Later he got involved in other causes, recorded the Tom Joad album, and eventually took part in first political campaigns, for Obama. He's even survived the fandom of David Brooks and Chris Christie. (h/t David Hazan)
And, for quite different experience, here's Jeff Katz's fictional imaginings of Bruce's misgivings before the album came out. Cameo by Bob Dylan.