Quick reaction to the proposed AUMF against ISIS
As previously discussed, the President already possesses the legal authority needed to conduct the anti-ISIS counter-terrorism campaign, which is not the same as a nation-v-nation war, such as Operation Iraqi Freedom. The President's counter-terrorism authority is rooted in Article II of the Constitution, not statutory authority, which has been affirmed by Congress since the Clinton administration. The proposed AUMF is for policy and political reasons, not for legal authority, although it may be legally useful for an anti-ISIS action on territory where the local nation opposes the action.
Repealing the 2002 AUMF (Public Law 107-243) would have limited impact since it was oriented on the threat posed by Iraq when Iraq meant Saddam's regime. At the same time, the 2002 AUMF was already redundant in terms of enforcing Iraq's compliance with the body of United Nations Security Council resolutions that set the terms of the Gulf War ceasefire. From the standpoint of the threat posed by Saddam's regime, there was closure on the 2002 AUMF since Saddam's regime is gone and the UN Security Council determined in 2010 that Iraq was largely in compliance with the UNSCRs. However, the UNSCRs for Iraq contain the overarching mandate to "restore international peace and security in the area" (UNSCR 678) and an argument can be proffered that UNSCR 2170 (2014) reactivated the authority of Public Law 107-243, which also contains a counter-terrorism character.
If the 2002 AUMF is repealed, the 1991 AUMF (Public Law 102-1) and sections 1095 and 1096 of Public Law 102-190 (1991) are still in effect. As far as I know, the UN authorization that P.L. 102-1 is predicated on, UNSCR 678 (1990), remains active, which means the US continues to be authorized "to use all necessary means to uphold and implement resolution 660 (1990) and all subsequent relevant resolutions and to restore international peace and security in the area" (UNSCR 678).
After the regime change of 2003, the Iraq Liberation Act of 1998 (Public Law 105-338), which mandated the post-war peace operations, moved to the forefront, and since the end of 2008, the US-Iraq relationship has been guided by the 2008-2011 Status of Forces Agreement and the overarching guidelines of the long-term Strategic Framework Agreement. Notice that President Obama did not propose an end-date for the SFA nor whatever SOFA he adopted with Iraq in 2014. Iraq-specific Public Law 102-1, sections 1095 and 1096 of Public Law 102-190, Public Law 105-235 (1998), and Public Law 105-338, counter-terrorism statutes Public Law 104-132 (1996) and Public Law 107-40 (2001), and of course, Article II of the Constitution have not been repealed, either.
There will be no repeat of Operation Iraqi Freedom because this time, the US is working with Iraq as an ally, not resolving a threat by Iraq as an enemy with noncompliant Saddam. President Obama's depiction of the mission for US forces in the anti-ISIS campaign seems similar to the mission envisioned had a residual US force stayed in 2011 to assist Iraqi forces. It's like Obama is taking a mulligan on the error of prematurely removing US peace-operation forces from Iraq. Of course, Iraq's condition now is very different than it was before Obama disengaged from Iraq. What would have been sufficient from a residual US force to protect Iraq then is likely no longer sufficient now.
Add: Legal analysis of the proposed AUMF at National Review and Lawfare blog. A balanced look at the conflicted nature of the proposed AUMF.
Add: S.J.Res.21 - Authorization for the Use of Military Force Against the Government of Syria to Respond to Use of Chemical Weapons, 06SEP13. Lawfare coverage.