The most striking example is the Kentucky Republican primary, in which the NRSC has chosen to throw most of their support behind the lackluster Trey Grayson, sponsoring a fundraiser and raising money for his campaign while ignoring Rand Paul who has led him in the polls by 15 points for almost six months. Grayson is using this money to run a very negative campaign and trying to smear Paul, all of which will hurt the Republican nominee in the general election. Despite this, Paul is crushing Grayson and is also favored to win the general election. And all the money and effort of the NRSC will have been wasted when it could have been used in a general election campaign where it would help defeat a Democrat rather than funding a struggle between two Republicans.
Similarly, in Florida the NRSC has chosen to throw their weight behind Governor Charlie Crist's campaign while ignoring the campaign of popular challenger Marco Rubio. As in Kentucky they are backing the wrong horse and Rubio's insurgent campaign is gaining ground on Crist. Again the NRSC will have wasted substantial amounts of money in a primary pitting one Republican against another instead of saving it for the general election in efforts to defeat the Democrats.
The same pattern is being repeated in Nevada where the NRSC anointed Sue Lowden and has helped raise money for her, ignoring a more appealing candidate in Danny Tarkanian, who has a higher overall favorability rating with the public. Lowden is more of a party insider, but has little else to recommend her, while Tarkanian has fresh ideas and comes from a business background and appeals more to independents and liberty-minded voters from the Tea Party movement. It's the same story in Indiana where they have chosen to back the bland and mediocre Dan Coats while ignoring John Hostettler who has more grassroots support and is running roughly even with him as well as polling better against the likely Democratic nominee.
The decisions made in these three races are particularly bad because these are races for seats which are open or where there is a weak Democrat incumbent and where candidates really ought to have been competing on an equal footing. Instead, the NRSC essentially picked one candidate out of the field of hopefuls and attempted to use their influence to give them a kind of artificial incumbent status, making poor choices and wasting a great deal of money in the process. Not only did they spend money fruitlessly but they also caused the candidates they opposed to spend more money, all of which could have been used against the Democrats in the fall.