I plan to pretend gas will be $2/gallon forever! LOL! OK seriously...
Step 1: Accept the realities of subsidy. Transport everywhere is subsidized massively by governments. You think user fees pay for the airport expansion? Not hardly. Highway taxes might pay the state/federal/interstate highway system, but they'd be useless without millions of miles of local roads your local taxes pay for. The only system that's ACTUALLY profit making is the freight railroad system in North America, because of deregulation.
Amtrak is actually an amazingly good deal for subsidy. Take an 800 mile Amtrak trip, you'll pay $85 and the government will subsidize $15 more. In Europe, you take an 80 mile trip, you'll pay $45 and the government will pay $55 more. We get a better deal because the service is so weak. Want better service? Subsidize it. It's cheaper if you consider the other stuff you DON'T have to build (e.g. airports, highway lanes, oil wars).
Once you do that, you're basically in like Flynn. People want high-speed-rail, just their grandparents don't want to pay for it and keep voting for "invest in foreign wars, not America" conservatives.
Second, America already has trains that go 125-150 between Boston and DC. So your Baltimore-DC line is in, grats! You can go much faster with trains you can pretty much just buy from France.
Third, it's just a question of the political will to roll them out in America, which would require a lot of rail construction. But it's very routine stuff... grading and bridges and eminent domain, like they've been doing for 150 years. Just a little straighter lol!
LA-Vegas is a stupid route, it would only work if it were subsidized by the casinos. That's been proposed, but they want to end the line on the east side of Cajon Pass, which means it does nothing for California traffic, leaves you without a car in Vegas, and is only a "goshy wow" sort of attraction like the Disney monorail.
All those other routes aren't going to happen. All the states will march to Washington, and hold out their hat for some of the $8B Federal high speed rail commitment. Their hats will all be empty. Their hats will be empty because the states aren't willing to "ante up" their share of the costs. Except for California, their hat contains $10 billion that the voters voted in 2008 (in the middle of the recession, note.) So the feds will give all the states a few hundred grand each to pay the staff in their high speed rail development office... and they'll throw the billions into California's hat. LA-SF, that's gonna happen even though it's the toughest route.