Amid rampant speculation that Vice President Joe Biden might jump into the race for the Democratic presidential nomination, Hillary Clinton shows there is not much room left in Iowa.

Less than two weeks after locking up the support of key Iowa Democrat former Sen. Tom Harkin, Hillary Clinton received the endorsement of perhaps the second most prominent democratic Iowan politician: Secretary of Agriculture Tom Vilsack.

“On Feb. 1, 2016 I intend to proudly caucus for Hillary Clinton — plain and simple,” Vilsack wrote in the first line of an op-ed published in the Cedar Rapids based paper The Gazette.

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Vilsack, who served as the 40th governor of Iowa from 1999 to 2007 and has been a cabinet member with Biden for the past seven years, endorsed Clinton early Tuesday evening ahead of the former secretary of state’s latest trip to Iowa.

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This get for the Clinton camp demonstrates how difficult a late entry into the 2016 contest would be for Biden, especially in Iowa.

Vilsack wrote that he supports Clinton for consistently fighting “to expand and strengthen the middle class,” and also emphasized that “loyalty” is one of the main reasons he will be caucusing for her.

“On a personal note, Hillary Clinton is one of the most loyal people I know and that is rare in politics,” he said in the op-ed.

There has also been speculation about Vilsack as a possible candidate for vice president in 2016 regardless of the eventual nominee.

In 2014, Biden told the Des Moines Register of Vilsack, “He’d make a great vice president because he does everything well. Look what he’s done for agriculture. I mean he is the single best secretary of agriculture. I’ve been here for eight presidents. There’s nobody that has been his equal.”

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Vilsack briefly ran for president in 2008, but ultimately dropped out and endorsed Hillary Clinton and become a national co-chair of her campaign.

Clinton’s Iowa state director this time around, Matt Paul, was a longtime Vilsack aide, previously working as communications director for the U.S. Department of Agriculture in Washington.

Mirroring the announcement of former Harkin’s endorsement less than two weeks ago, the op-ed arrived just before Clinton lands in Iowa for a three-event day on Wednesday. The Clinton campaign said that Vilsack will be with the candidate as she travels to Sioux City, Ankeny, and Baldwin.

This article first appeared at NBCNews.com