Lawyers at the nation’s biggest law firms are voting with their wallets — and Barack Obama is the clear winner.

His biggest supporters? Lawyers at DLA Piper, who have given Obama more than $345,000 in direct campaign donations as of September 21, according to data from the nonpartisan Center for Responsive Politics and its website, Opensecrets.org.

Overall, lawyers at the 20 biggest firms have given Obama $1.9 million this election cycle, versus just over $1 million to Mitt Romney.

Romney’s biggest fans based on contributions are at Kirkland & Ellis, where lawyers have donated $338,000 (the numbers do not include contributions to political action committees). Of the nation’s 20 biggest firms, Kirkland is one of just five where employees have given more in direct contributions to the Republican challenger than the Democratic incumbent. The others are White & Case, Morgan, Lewis & Bockius, Weil, Gotshal & Manges and Gibson, Dunn & Crutcher.

In fact, Kirkland’s 1,400 lawyers have given the most money, period, also directly donating $118,000 to Obama. A firm spokeswoman could not immediately be reached for comment. Under federal election laws, individuals may donate $2,500 per candidate per election.

Donations at firms where Obama supporters predominate tend to be lopsided. For example, for every one dollar DLA Piper employees donated to Romney — $32,750 in all — Obama collected more than 10. A spokesman for DLA Piper, the second-biggest law firm in the country based on headcount, could not immediately be reached for comment.

Still, that’s nothing compared to the most partisan big firm based on donations — Cleary, Gottlieb, Steen and Hamilton, where Obama has raised $81,000 and Romney just $3,750 — a 21 to 1 difference.

By comparison, at Morgan, Lewis & Bockius, Romney has raised $81,000 and Obama is not far behind with $62,000. At White & Case, Romney donations of $33,000 topped Obama’s by just $7,000.

At Sidley Austin, where onetime summer associate Barack Obama met Michelle Robinson, firm lawyers have given the incumbent president $274,000. Romney has pulled in a respectable $95,000.

Baker & McKenzie, the nation’s biggest law firm with about 3,800 lawyers, is not exactly a hotbed of political activity — not surprising, considering 80 percent of firm lawyers practice outside the United States. Firm lawyers have given just $55,000 to Obama and $14,000 to Romney.

At Hogan Lovells, with 2,250 lawyers, donations are also muted — $87,000 for Obama, $42,000 for Romney.

Lawyers at somewhat smaller Washington firms have been more active. Wilmer Cutler Pickering Hale and Dorr’s 900 lawyers have given Obama $168,000 and Romney $34,000. At Covington & Burling, with just over 700 lawyers, Obama donations total $114,000 versus $40,000 for Romney. Arnold & Porter’s 675 attorneys skew hard for Obama, giving him $152,000, compared to just $11,000 for Romney.

Among other top-20 firms, Jones Day attorneys gave $167,000 to Obama and $95,000 to Romney; Latham & Watkins favored Obama $133,000 versus $59,000 for Romney; Skadden, Arps, Slate, Meagher & Flom lawyers gave $119,000 to Obama and $52,000 to Romney.

The prize for most apolitical firm goes to Squire Sanders. The firm’s 1,200-plus lawyers have given a grand total of $15,000 to Obama and $3,000 to Romney.

Contact Jenna Greene at jgreene@alm.com.