Donnelly proved himself a tough campaigner by hanging onto a Republican-leaning seat in the GOP wave election in 2010, although his fundraising so far has been less than stellar: he raised just $220,000 last quarter and had $850,000 in the bank.
Despite the polling, national Republicans argue either candidate will have an easy time against Donnelly.
Lugar has been beset by problems this month, some of them
self-inflicted: he's repeatedly struggled to get past questions about
his residency that stem from him not owning a home in Indiana for
decades. The National Rifle Association has also endorsed Mourdock,
giving Lugar additional issues on the right besides his Tea Party
The primary is in early May. The poll was conducted March 12-15 by the Democratic-affiliated Global Strategy Group.