Greg Sargent: “Democrats who are trying to get an initiative raising the minimum wage on the ballot in Arkansas tell me they have now collected more than the requisite number of signatures — which, if certified, could boost turnout for Dem Senator Mark Pryor, possibly helping determine control of the Senate in this fall’s elections.”

“A minimum wage ballot initiative could give Pryor a turnout boost among core voter groups who tend to drop off in midterms, and any single race could sway the battle for the Senate.”

A new Public Policy Polling survey in Pennsylvania finds Tom Wolf (D) leading Gov. Tom Corbett (R) by a whopping 25 points, 55% to 30%.

A new Public Opinion Strategies (R) poll in Arkansas finds Tom Cotton (R) with a small lead over Sen. Mark Pryor (D), 46% to 41%.

First Read notes that “if Democrats get any kind of opening in Mississippi, here’s why that would be very important in November: A Democratic win there — as remote as it may seem — would raise the GOP’s magic number (from six to seven) in the seats it must net in order to win back the Senate. Given the stakes, you are going to see a lot of pressure on the Lotts and Barbours to get on board if McDaniel wins. Then again, it’s very possible Cochran holds on. This is a 50%-50% race, folks.”

National Journal: “The Senate race to succeed retiring Democratic Sen. Tim Johnson could have been one of the most consequential contests in the country, if Democrats had a little more luck. Just over a year ago, the political talk in South Dakota centered on which of their up-and-coming prospects would run–former Rep. Stephanie Herseth Sandlin, one of the most popular figures in the state after representing it for three full terms in the House, or Tim Johnson’s son Brendan Johnson, who’s serving as a U.S. attorney.”

“As Senate Majority Leader Harry Reid and the Democratic Senatorial Campaign Committee tried to engineer the situation to their advantage–they preferred Herseth Sandlin to the more-liberal Johnson, and wanted to avoid a contentious primary–the party’s worst-case scenario materialized. Johnson first expressed his disinterest in May 2013, leaving the door wide open for the former congresswoman to run. At the same time Johnson made his decision, Weiland announced his candidacy with support from some Johnson allies.”

“What Chris McDaniel is trying to do Tuesday – defeat an incumbent U.S. senator from Mississippi – would be almost unheard of in the state’s history,” the Northeast Mississippi Daily Journal reports.

“If McDaniel prevails against long-serving Sen. Thad Cochran in Tuesday’s Republican primary, it would mark the first time since 1942 an incumbent from Mississippi lost a U.S. Senate race. That year Jim Eastland defeated incumbent Wall Doxey, who had won a special election in 1941 after the death of Sen. Pat Harrison.”

Clarion Ledger: “Voters say contentious races are not new to Mississippi, but they can’t remember a Senate race that has been so nasty.”

“Up until about a month ago, Marco Rubio had steered clear of Republican primaries, avoiding antagonizing one wing of the party or the other when he’s probably going to need them both come 2016,” Politico reports.

“Then along came the Iowa Senate primary. It featured a candidate with rare appeal to both wings of the party, in an early presidential voting state where Rubio needs to gain traction if he’s going to run for president. So the Florida Republican senator made an exception: He has gone all in for Joni Ernst, dropping $210,000 in independent expenditures on the Iowa state senator’s behalf and stumping with her Monday in the Des Moines area on the eve of her Tuesday primary for the Senate GOP nomination.”