Bernie Sanders now has hard numbers — in dollars and donors — to back up the idea that he can run a serious campaign for the Democratic presidential nomination in 2016.

The Vermont senator banked $15 million, a surprisingly robust fundraising haul, in the three months that ended June 30. It's one-third of the $45 million that Hillary Clinton hauled in for the second fundraising quarter of the year. But the number of donors — 250,000 — suggests Sanders will be able to go back to the well to keep his campaign running.

And that means Clinton won't be able to dispatch him anytime soon.

The numbers track with the strategy senior Sanders adviser Tad Devine outlined in a recent interview with Vox. The campaign hopes to end the year with 1 million contributors and do well enough in the Iowa caucuses and New Hampshire primaries to entice them into giving again and again, Devine said.

"I am more than aware that my opponents will be able to outspend us. But we are going to win this election," Sanders told a Madison, Wisc., crowd of 10,000 — the largest for any presidential candidate so far this cycle — Wednesday. "They may have the money but we have the people. And when the people stand together, we can win."

The contribution totals include money from folks who bought bumper-stickers, T-shirts and other campaign swag, according to a Sanders release e-mailed to reporters.

$15 million isn't bad, but it doesn't make him Jeb Bush or Hillary Clinton

The $15 million haul is even more impressive given that Sanders announced his campaign a third of the way through the quarter and held his official launch event in the last week of May. And yet it is still small enough that it would be foolhardy to compare his insurgent campaign to that of Barack Obama's in 2008. Obama was able to surpass Clinton's fundraising for the first time in the comparable second quarter of 2007.

Clinton advisers have said her goal is to raise $100 million by the end of the year, a bar that appears to be pretty easy for her to clear. Sanders has set a target of $40 million to $50 million, according to Devine, far short of what either Clinton or Obama raised in the first year of the 2008 campaign.

But Sanders' big fundraising quarter promises to outpace some of the Republican candidates, and it's more than the nearly $14 million John Edwards snagged in the final quarter of 2007 before he exited the 2008 campaign.

More important, it's a show of strength in numbers that dovetails well with Sanders' populist message and the surge he's getting from big crowds on the campaign trail. And it comes at a time when Sanders is gaining ground on Clinton in Iowa, the first caucus state, according to a Quinnipiac University poll released Thursday.

The bottom line: It's been a damn good week for Bernie Sanders, and he's stocking away enough cash to ensure that he can run a big-league campaign.