Tuesday's presidential and congressional primaries in Pennsylvania, Maryland and three other states turned out about as well as they possibly could for Senate Democrats, for three big reasons:

1. Their preferred candidate won in Pennsylvania

Senate Democrats spent more than $1 million and trotted out Vice President Biden to help Katie McGinty beat former congressman Joe Sestak in what looked to be a tight Pennsylvania Senate Democratic race Tuesday. The investment of time and money underscored their hopes that she has the best chance of the two at ousting Sen. Pat Toomey (R) in November and helping Democrats win back control of the Senate.

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The gamble worked. McGinty has her struggles (like fundraising and some underwhelmed Democratic supporters in Pennsylvania), but she comes from a working-class background and would be the state's first female senator. Perhaps just as important is what she doesn't have: She doesn't have a losing record to Toomey like Sestak does (he lost the Senate race in 2010) nor bad blood among Senate Democrats for repeatedly going against their wishes. Senate Democrats can rightly say they got their best nominee -- and they saved some face along the way, too.

2. They've got a potential new leader in Chris Van Hollen

On the whole, Senate Democrats officially stayed neutral in Maryland's primary race for the open seat. But they privately wanted Rep. Chris Van Hollen to beat Rep. Donna Edwards, a fiery liberal who is is not as well liked as Van Hollen on Capitol Hill. (Not everyone was so private about it. "Chris Van Hollen is the kind of legislator who makes things happen," said Senate Minority Leader Harry Reid (D-Nev.) when he endorsed Van Hollen.) Van Hollen did win, and he's likely to win the heavily blue Senate seat in November.

Van Hollen has got a made-for-Senate resume. The progressive Democrat has been a key ally of Nancy Pelosi, he ran the House Democrats' campaign arm in the 2008 and 2010 elections and is the top Democrat on a key House Budget Committee. Van Hollen's political future seems so bright that Pelosi tried to persuade him to stay in the House to potentially take her place as leader. Senate Democrats will certainly welcome a guy with such drive and promise to their ranks.

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3. Donald Trump looks like the GOP nominee

More and more, it seems like Senate Democrats' good fortunes are also tied to the GOP presidential front-runner's fortunes. And it was a really great night for Trump. He decisively won all five states. "I consider myself the presumptive nominee," he said Tuesday from the gleaming Trump Tower in New York.

Trump had good reason to brag: Politics and math are on his side now as much as ever. He's making strides toward the delegate total that will allow him to enter the convention in Cleveland and argue the majority of GOP primary voters chose him. (You need 1,237 delegates to become the Republican nominee.) It's also increasingly difficult for Trump's rivals, Sen. Ted Cruz (Tex.) and Ohio Gov. John Kasich, to beat him in contests before then -- quixotic truce and all.

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Let's tie this back to Senate Democrats. If Trump is the nominee, he will be the most unpopular presidential candidate since the former head of the Ku Klux Klan, according to Washington Post-ABC News polling. Seven in 10 women view Trump negatively, according to recent NBC News-Wall Street Journal polling. So do 3 in 4 millennials and 4 in 5 Hispanics.