Election fundraising is about more than what candidates raise for their campaigns. Increasingly, candidates are aligned with super PACs and other outside groups that assist the campaigns but can’t coordinate directly with candidates. Because super PACs don’t face the $2,700-per-election limit that applies to campaigns, they can raise money more efficiently, tapping just a few donors for large donations.

through the second quarter

All donors Gave to multiple candidates

Some 66 companies or individuals have made donations of $1 million or more to super PACs aligned with candidates. Search below for their donations to PACs and campaigns:

Allies of Republican Jeb Bush and Democrat Hillary Clinton have been the strongest fundraising forces of the election cycle so far in their respective parties. But Mr. Bush’s fundraising has been heavily concentrated in his affiliated super PAC, while the bulk of Mrs. Clinton’s money has gone to her campaign. Since a campaign can solicit donations of only $2,700 per individual for a primary election, that leaves her less reliant on million-dollar donors than Mr. Bush.

The super PAC aligned with former Florida Gov. Jeb Bush raised $103 million in the first half of the year, far surpassing any other super PAC supporting an individual 2016 candidate. To do so, the group relied heavily on millionaires, whose donations accounted for more than a quarter of the super PAC’s overall haul. Here’s a look at who else raked in the most million-dollar donations through the first half of the year:

Some candidates have been heavily reliant on large-dollar donors to friendly super PACs. The PACs have traditionally been most effective in airing TV ads on a candidate’s behalf, but this cycle they’re taking on some roles traditionally performed by campaigns, such as coordinating volunteers and working with the press. For these candidates, a majority of combined campaign and super PAC fundraising came from donations of at least $1 million:

On the other side of the equation are candidates who have been largely bankrolled by donations of $200 or less. The level of small-dollar donations is often read as a sign of grassroots enthusiasm. Candidates who rely heavily on small donations have a key advantage: They can continue to tap the same donors for more money, while campaigns whose donors have hit the legal donation limit must find new donors to grow their war chests.

Industry support for a candidate sometimes signals that their policy interests are aligned. It's also often a reflection of where that candidate's experience lies.Top industries donating to each candidate or their aligned super PAC, as of most recently available data:

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Jeb Bush Industry Amount Securities & Investment $31,356,814 Oil & Gas $9,840,160 Retired $9,346,895 Real Estate $9,166,367 Misc Finance $6,463,770

Hillary Clinton Industry Amount Retired $7,431,164 Lawyers/Law Firms $6,986,456 TV/Movies/Music $6,472,676 Securities & Investment $5,435,805 Women's Issues $2,970,700

Mrs. Clinton has major appeal in Hollywood and on Wall Street.

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Ted Cruz Industry Amount Real Estate $25,729,192 Securities & Investment $11,794,055 Retired $3,142,703 Lawyers/Law Firms $688,038 Misc Finance $674,038

Marco Rubio Industry Amount Automotive $5,082,630 Electronics Mfg & Equip $3,127,292 Health Professionals $2,816,462 Retired $2,384,533 Securities & Investment $1,948,191

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Mr. Carson, a retired neurosurgeon, drew many contributions from health professionals.

Ben Carson Industry Amount Retired $5,239,764 Health Professionals $539,535 Real Estate $279,236 Misc Business $276,591 Republican/Conservative $266,539

Chris Christie Industry Amount Securities & Investment $4,866,504 Retired $1,088,849 Non-Profit Institutions $1,027,050 Commercial Banks $777,520 Real Estate $722,688

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Rand Paul Industry Amount Securities & Investment $2,869,747 Electronics Mfg & Equip $1,183,701 Retired $828,699 Real Estate $321,360 Health Professionals $259,650

Carly Fiorina Industry Amount Business Services $1,638,243 Retired $1,444,557 Republican/Conservative $1,059,352 Securities & Investment $383,270 Real Estate $326,111

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Mike Huckabee Industry Amount Poultry & Eggs $3,002,700 Recreation/Live Entertainment $509,672 Retired $383,712 Real Estate $113,465 Oil & Gas $82,200

Lindsey Graham Industry Amount Securities & Investment $1,878,750 Recreation/Live Entertainment $512,300 Retired $491,207 Lawyers/Law Firms $275,677 Real Estate $268,511

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Critics of Mrs. Clinton have drawn contrasts between her top donors and those of Mr. Sanders. Where she is popular on Wall Street, he drew heavily from the education sector.

Bernie Sanders Industry Amount Retired $862,896 Education $470,077 Lawyers/Law Firms $268,469 Health Professionals $264,086 Misc Business $259,724

Bobby Jindal Industry Amount Oil & Gas $1,301,000 Securities & Investment $465,650 Sea Transport $275,800 Health Services/HMOs $235,522 Business Services $168,750

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Martin O'Malley Industry Amount Lawyers/Law Firms $391,778 Retired $268,058 Real Estate $159,150 Beer, Wine & Liquor $150,030 Health Services/HMOs $117,612

John Kasich Industry Amount Retired $607,774 Lawyers/Law Firms $208,422 Real Estate $113,950 Misc Finance $78,650 Business Services $71,688

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George Pataki Industry Amount Retired $137,450 Real Estate $90,000 Misc Business $84,900 Oil & Gas $80,400 Health Professionals $53,350

Rick Santorum Industry Amount Retired $235,992 Misc Finance $145,850 Lawyers/Law Firms $37,850 Misc Manufacturing & Distributing $28,400 Securities & Investment $24,600

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Donald Trump Industry Amount Retired $259,555 Automotive $91,839 Health Professionals $42,538 Misc Business $38,676 Real Estate $25,521