Maureen Groppe | IndyStar

Democratic Sen. Joe Donnelly is coming off the best fundraising quarter of his political career, while the three Republicans vying for the chance to knock him off this fall are still locked in a hotly contested primary bid.

Donnelly raised $1.63 million in the first three months of the year and had $6.4 million in the bank at the end of March, his campaign announced Sunday.

His previous highest haul of $1.55 million was set in the third quarter of the 2012 election, right before he defeated Republican Richard Mourdock after spending nearly $5.6 million.

Hoosier Politics newsletter: What's happening in politics across Indiana

As Indiana’s only statewide-elected Democrat in a state President Trump carried by 19 percentage points, Donnelly is top GOP target in this year’s election.

He’s not, however, raised as much money as some of the other Democrats facing tough re-election bids.

While public filings for the first quarter reports won’t be available until later this month, the $5.3 million Donnelly had in the bank at the start of the year was less than the stashes of Democratic incumbents in Missouri, Ohio, Montana and Wisconsin.

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In Missouri, for example, which is similar in population size to Indiana, Democratic Sen. Claire McCaskill had $9 million in cash at the start of the year after raising nearly twice as much as Donnelly in 2017.

But Donnelly could benefit from the ongoing infighting among Indiana Republicans.

The GOP primary is a bitter, spirited contest between Rep. Todd Rokita, Rep. Luke Messer and former state House Rep. Mike Braun. Through mid-March, the Republicans had aired more commercials than in any other Senate race in the country, according to the independent Wesleyan Media Project.

Some of the ads have attacked the other GOP candidates, leading to some hand-wringing among Republicans who fear the eventual winner will be a weakened general election candidate.

Michelle Pemberton/IndyStar photos

None of the Republican contenders has announced how much they raised in the first quarter. Rokita and Messer were closely matched on fundraising last year, despite the greater support Messer has received from top Indiana Republicans. But an outside group with ties to Vice President Pence has spent more than $300,000 on ads supporting Messer, giving him an overall financial advantage over Rokita.

Braun, who is largely self-funding his campaign, led both Rokita and Messer in campaign dollars.

Donnelly last year significantly outraised all three Republicans in total dollars, as well as in the small dollar contributions that can indicate grassroots enthusiasm. Donnelly collected $642,767 from people who gave less than $201. Rokita raised $55,090 from small dollar contributors. Messer raised $36,491. Braun raised $8,043.

Although Donnelly has not had to spend money on a contested primary, the winner of the GOP nomination is not likely to lack resources for the general election. The national parties and super PACs are expected to bombard Indiana with advertising.

Americans for Prosperity, an advocacy group founded by the billionaire Koch brothers, has already spent about $4 million criticizing Donnelly for voting against the GOP tax package, after spending nearly $2 million urging him to vote for it.