In January, the US Olympic Committee announced that Boston was its first choice to be host city for the summer games in 2024. Los Angeles was number two. But on Monday, Boston dropped out, leaving the Committee until mid-September to come up with a substitute.Los Angeles has venues left over from 1984 — and, there are warm memories of the only city ever to profit from hosting the games. But, can Mayor Eric Garcetti promise what Boston would not: that taxpayers will cover cost overruns or revenue losses? He’s got six weeks to decide — and public opinion could be crucial. Meanwhile, US Committee members are in Kuala Lampur, where the International Committee is meeting. Robert Livingstone is there, too. He's an Olympic historian and a journalist, who’s covering the process for GameBids.com.