Sen. Amy KlobucharAmy Jean KlobucharKlobuchar fundraises for McConnell challenger: 'Two Amys are better than one' The Hill's 12:30 Report: Trump digs in ahead of House vote to condemn tweet The Hill's Morning Report - Presented by JUUL Labs - House to vote to condemn Trump tweet MORE (D-Minn.) is the most popular senator running for reelection, while Joe Lieberman (I-Conn.) is the least, according to new polling data.

Public Policy Polling (PPP), a Democratic-leaning firm, looked at the approval ratings for 59 senators during the second half of 2010, and several of them will face voters in 2012. The senators were ranked by the spread between their approval numbers and disapproval numbers.

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Of the 59, Klobuchar is the most popular, with an approval rating of 59 and a disapproval of 29 (a 30-point spread), while Lieberman has an approval rating of 33 and a disapproval of 54 (a 21-point spread).

Lieberman hasn't said what he'll do in 2012, but Klobuchar is preparing for rivals, including a possible challenge from Tea Party darling Rep. Michele BachmannMichele Marie BachmannKlobuchar urges CNN town hall audience: 'That's when you guys are supposed to cheer, OK?' Michele Bachmann praises Trump: Americans will 'never see a more godly, biblical president' Will Biden lead a 'return to normalcy' in 2020? MORE (R-Minn.).

Coming in second was Sen. Scott Brown (R-Mass.), who's also up in 2012. He had a 53 percent approval and 29 percent disapproval (a 24-point spread). Sen. Judd Gregg (R-N.H.), who is retiring, was third, and Sen. Olympia Snowe (R-Maine), also up in 2012, was fourth, with a 56 percent approval and 34 percent disapproval (a 22-point spread).

Of other senators up in 2012, near the bottom were Sens. Claire McCaskillClaire Conner McCaskillTrump nominees meet fiercest opposition from Warren, Sanders, Gillibrand Feds allow campaigns to accept discounted cybersecurity services GOP frets over nightmare scenario for Senate primaries MORE (D-Mo.) — 43 approval/44 disapproval; Bob CaseyRobert (Bob) Patrick CaseyCrucial for Congress to fund life-saving diabetes research Republicans make U-turn on health care Democrats press IRS on guidance reducing donor disclosure requirements MORE Jr. (D-Pa.) — 36 approval/40 disapproval; and John Ensign (R-Nev.) — 41 approval/48 disapproval.
   
Retiring Sen. Roland Burris (D-Ill.) came in last, with a 19 percent approval rating and a 58 percent disapproval rating.

PPP's Tom Jensen notes in his analysis that "the average approval rating for a senator right now is 43 percent approving to 40 percent disapproving" and that "there's very little difference in the average approval of Republican senators versus Democratic senators." The average GOP senator had a 43/37 split, while the average Democrat rated a 44/41. 

Several senators up for reelection came in under the 50 percent approval mark, including: Sens. Ben CardinBenjamin (Ben) Louis CardinCan new US Strategy on Women, Peace & Security give women a real seat at the table? Ask Afghan women Maryland lawmakers slam 'despicable' Trump remark about journalists on newsroom shooting anniversary Democrats leery of Sanders plan to cancel student loan debt MORE (D-Md.), Kay Bailey Hutchison (R-Texas), Tom CarperThomas (Tom) Richard CarperFighting the opioid epidemic: Congress can't just pass laws, but must also push to enforce them Overnight Energy: Scientists flee USDA as research agencies move to Kansas City area | Watchdog finds EPA skirted rules to put industry reps on boards | New rule to limit ability to appeal pollution permits Watchdog finds EPA skirted rules when appointing industry leaders to science boards MORE (D-Del.), Jon Kyl (R-Ariz.), Jim Webb (D-Va.), Kirsten GillibrandKirsten Elizabeth GillibrandThe Hill's 12:30 Report: Trump digs in ahead of House vote to condemn tweet 'Game of Thrones' scores record-breaking 32 Emmy nominations The Hill's Morning Report - Presented by JUUL Labs - House to vote to condemn Trump tweet MORE (D-N.Y.), Sherrod BrownSherrod Campbell BrownThe Hill's Morning Report - A raucous debate on race ends with Trump admonishment On The Money: Senators unload on Facebook cryptocurrency | Tech giants on defensive at antitrust hearing | Democrats ask Labor Department to investigate Amazon warehouses Hillicon Valley: Senators unload on Facebook cryptocurrency plan | Trump vows to 'take a look' at Google's ties to China | Google denies working with China's military | Tech execs on defensive at antitrust hearing | Bill would bar business with Huawei MORE (D-Ohio), Bill NelsonClarence (Bill) William NelsonDemocrats target Florida Hispanics in 2020 Poll: Six Democrats lead Trump in Florida match-ups How Jim Bridenstine recruited an old enemy to advise NASA MORE (D-Fla.), Maria CantwellMaria Elaine CantwellFAA nominee advances to full Senate vote Women lawmakers to play in Congressional Baseball Game following Title IX anniversary Hillicon Valley: Democratic state AGs sue to block T-Mobile-Sprint merger | House kicks off tech antitrust probe | Maine law shakes up privacy debate | Senators ask McConnell to bring net neutrality to a vote MORE (D-Wash.) and Debbie StabenowDeborah (Debbie) Ann StabenowGOP Senate challenger in Michigan raises .5 million in less than a month It's time to let Medicare to negotiate drug prices Trump judicial nominee says he withdrew over 'gross mischaracterizations' of record MORE (D-Mich.).