WASHINGTON, D.C. — Sen. Charles Grassley told reporters Wednesday that Sen. Barack Obama’s clinching of the Democratic presidential nomination is a seminal moment in American history.

And he thinks Obama could do worse than to choose Sen. Hillary Clinton as his running mate.

Grassley, Iowa’s senior senator and a Republican, said Obama’s win is a major step forward for a diverse society. Obama is the first black candidate to be the presidential nominee for one of the country’s major political parties.

“Over the long term it’s going to advance diversity in the country,” Grassley said. “He’s going to have a legacy whether he’s president or not, and a very worthy legacy.”

That said, Grassley still isn’t likely to vote for Obama in November. He’s hoping John McCain, a fellow Senate Republican, can unify Republicans and keep the party’s hold on the White House.

Recent results are not encouraging for Republicans. The party has lost several seats in areas that were conservative bastions for decades, and Democratic candidates raised far more money during the primary process than Republicans.

McCain has struggled to unify the party. He is viewed with suspicion by some conservatives, a fact that former rival Mike Huckabee took advantage of as he continued to campaign after McCain became the all-but-inevitable nominee. But Grassley believes McCain is the key to rebuilding party unity. He called the situation difficult but not hopeless.

“Only John McCain can save us,” from an election disaster, he said. To Grassley, that means McCain must restore fiscal responsibility for the party. “He’s going to [have to] show that Republicans are going to act like Republicans.”

McCain has not announced a vice presidential candidate. The Midwest is shaping up as a critical battleground in the general election. Grassley favors a midwesterner for the bottom half of the ticket and mentioned Minnesota Gov. Tim Pawlenty as a possible candidate.

Obama is also looking for a vice presidential candidate. Clinton has pointedly left herself open to the idea in recent days. While some pundits say the match would hurt Obama, Grassley isn’t so sure. He pointed to Clinton’s strong showings among women.

“It probably would help because [Obama] is short of getting votes on women,” he said.

And Grassley thinks people might be tempted to make a mistake and discount the Clinton name after the primaries. Former Pres. Bill Clinton is widely viewed as having alienated some of the Democratic Party’s core blocs with his comments during his wife’s campaign. Grassley offered a more nuanced picture.

“I don’t know how to assess it, because he’s been out of office for eight years,” Grassley said. Clinton still receives warm welcomes from many Democrats and retains popularity among many segments of the party. “I think there’s still a tendency to underestimate what he might do for the Democratic cause.”

Matt Milner can be reached at (641) 683-5359 or via e-mail at mwmilner@mchsi.com