Last week a Sift-reading friend told me she had set aside some money to contribute to Senate candidates, and wondered where I thought it would be best spent.

We agreed that this is a good time to contribute. In general, early money is more valuable than late money, but (if you’re like me) you’d usually rather see your money spent in the general election than during the primary. So one of best times to contribute is right after the primaries bring the race down to a Democrat vs a Republican.

There are 33 Senate races this year, but a few simple criteria will narrow down the candidates worth contributing to or volunteering for.

I’ve never claimed to be non-partisan. (I try hard to keep the Sift honest, but I’m not trying to be neutral. I write what I believe, not just what I want you to believe.) So it shouldn’t surprise anybody that my first criterion is that I’m only considering candidates who will caucus with the Democrats. (That would include independents like Bernie Sanders of Vermont and probably Angus King of Maine.) Anybody committed to vote for Mitch McConnell as majority leader is off my list.

Second, the race should be close. I love Bernie Sanders, but I expect him to win with or without me. Real Clear Politics currently rates 8 races as toss-ups: Florida, Massachusetts, Missouri, Montana, Nevada, North Dakota, Virginia, and Wisconsin.

Whether that’s your serious-support list or not depends on how optimistic/pessimistic you are about what will happen between now and November. If you expect a big Democratic surge that isn’t showing up in the polls yet, then you might want to reach for one of RCP’s “leans Republican” seats, like Arizona, where Richard Carmona currently trails by about 11%. If you expect the opposite, you might want to defend one of the “leans Democratic” candidates, like Sherrod Brown in Ohio, ahead by 8%.

I don’t really have a hunch about the trend, so I’ll stick with the toss-ups. Next, I want strong progressive voices in the Senate. I want somebody who’s going to make me proud, not just be slightly better than a Republican. That takes Bill Nelson of Florida (not to be confused with Ben Nelson of Nebraska, who is worse) off my list. He has a history of joining Republicans on issues like eliminating the estate tax, and he’s generally one of the last Democrats to get on board for things like raising the debt ceiling. So, Bill, I’ll be rooting for you on election night, but I can think of people more deserving of my time and money.

Two candidates that jump right out at me are Elizabeth Warren in Massachusetts and Tammy Baldwin in Wisconsin. Both of them will face an avalanche of out-of-state money, Warren from the financial industry and Baldwin from the religious right.

Elizabeth Warren. Warren you’ve probably heard of, even if you’re not from Massachusetts. I first noticed her when she was chair of the Senate’s TARP Oversight Committee. She did several very plain-spoken, hard-hitting interviews on Rachel Maddow’s show where she laid out exactly how opaque the program was and how few of the underlying problems were being fixed.

The best argument for putting Warren in the Senate was the Jamie Dimon testimony to the Senate Banking Committee. (More about that in the Nuggets.) Warren is exactly the person who should have been in that room.

She’s a Harvard law professor, so her opponent Sen. Scott Brown is trying to tar her with the Harvard elitist label. But she wasn’t born into the Harvard strata of society, she started in the working class and climbed the ladder. She understands ordinary people and wants to be in a position to watch their backs.

Current polls are about as close as polls can be: Brown 43.8%, Warren 43.5%. I expect Warren to win a close race for three reasons: Undecideds have a tendency to break against the incumbent, Massachusetts is a blue state, and Warren’s supporters are genuinely enthusiastic about her. But Wall Street really hates Warren, so Brown will have a lot of money to spend.

Tammy Baldwin. Unless you live in Wisconsin, you may not know much about Tammy Baldwin. She’s been in Congress for 14 years, and is the only openly lesbian congresswoman. (She was already out of the closet when she ran in 1998. Up until that time, the only gay representatives had come out while in office.) In 2010, National Journal’s ratings had her tied for being the most liberal member of the House.

Now, my first thought on hearing those facts would be: She’s going to get crushed. But so far that’s not happening. The Republican primary isn’t until August, and the RCP average has her trailing former Governor Tommy Thompson by 8.7%. But that average is skewed by a Rasmussen poll with a huge Republican bias (Thompson ahead 52%-36%). The other two polls have her behind Thompson by manageable numbers: 4% and 6%, which could just be name recognition. Marquette University’s poll has her ahead of the other two likely Republican candidates.

There’s also no guarantee Thompson wins the primary, or gets through unscathed with the Club for Growth gunning for him. Chuck Todd sums up the race and interviews Baldwin:

Other toss-up Democrats. Claire McCaskill isn’t exactly an inspiring progressive voice. (National Journal rates her exactly in the middle as the 50th most liberal senator.) But this is Missouri we’re talking about; what did you expect? I think she’s doing as much as the voters will allow, and that holding this seat is key to holding the Senate. Polls: Rasmussen has her behind by double digits, but PPP says the race is tied.

Jon Tester in Montana is another incumbent Democrat in a Republican state. Don’t expect his support on, say, gun control. But his heart is in the right place when it comes to keeping Wall Street in check. PPP and Rasmussen disagree about who is ahead.

Immigration is likely to be a huge issue in the Nevada race. Shelley Berkley is challenging the incumbent Dean Heller, who was appointed when John Ensign resigned in disgrace. Nevada is a swing state that’s been trending blue as the Hispanic vote increases, but Republicans keep offering far-right candidates. Heller is a typical senate Republican, rated the 73rd most liberal senator. Berkley supports the DREAM Act; Heller wants to build a bigger border fence. The non-Rasmussen polls have this as a neck-and-neck race.

In Virginia, Tim Kaine vs. George Allen is a marquee match-up. Kaine has been governor and Allen senator. (Allen famously lost to Jim Webb in 2006 after the Macaca gaffe.) So far, I haven’t found anything thrilling on Kaine’s web site, and he seems to be running a vague I-was-a-good-governor campaign. But he’s narrowly ahead in the swingiest of swing states.

I confess I had never heard of North Dakota candidate Heidi Heitkamp until this morning. She’s running in a red state as a former state attorney general who fights for the people. Her web site is focused on local North Dakota issues, and I really have no idea how progressive she’d be. (She favors the Keystone Pipeline that environmentalists oppose.) Polls have her neck-and-neck with Rep. Rick Berg.