Here are the 2018 campaign's biggest individual donors – so far

Jahi Chikwendiu | The Washington Post | Getty Images

Tom Steyer holds one of his Need to Impeach town hall meetings on March 20, 2018, in Largo, Md.

Individual campaign contributions this year are concentrated mostly among just a handful of rich donors, according to the latest campaign finance data.

With the first quarter just ended, the 100 biggest individual donors to the upcoming House and Senate elections have contributed a combined $154 million, according to a tally of campaign finance records by the Center for Responsive Politics. Of that amount, roughly half came from just the top 12 donors on the list.

Overall, about two-thirds of all individual political campaign contributions have come from one-quarter of 1 percent of American voters.

About 30 percent of that money went directly to candidates running for office. The rest, so-called soft contributions, went to groups that spent indirectly on behalf of individual candidates, the CRP data show.

The top 100 donors tilt toward Republican and conservative candidates, according to the CRP. So far, about $83 million has been spent on right-leaning candidates, compared with $65 million for Democrats and liberals.

The biggest individual Republican donor, by a healthy margin, is Richard Uihlein, a Chicago businessman who founded a shipping company with his wife in 1980 after working for a family packaging business founded by his father.

So far in this election cycle, Uihlein and his wife have contributed more than $21 million to Republican and conservative candidates. Since 2010, Uihlein has given nearly $50 million to political organizations, according to Federal Election Commission records compiled by Ballotpedia.

The second biggest individual donor, Tom Steyer, has spent nearly $16 million in the current cycle to support Democratic and liberal candidates, according to CRP. Steyer, a San Francisco investor who retired in 2012 to focus on politics, spent more than $73 million in 2014 and roughly $100 million in 2016, according to Ballotpedia. Steyer is also leading an initiative called Need to Impeach, which is geared toward influencing Congress to impeach President Donald Trump.

So-called outside spending – money spent to favor one party or another without giving it directly to a candidate – has become the preferred conduit for campaign contributions, totaling roughly $1.4 billion in the 2016 election cycle.

As of the end of the first quarter, these "independent expenditures" amounted to about $88 million, the CRP reports. That amount doesn't include so-called dark money contributions, which are not required to be reported to the FEC.

Among the top 100 individual donors, about 70 percent of their money, or about $108 million, went to outside spending groups.

Here's a look at where the top individual donors have made their contributions, so far.