Under fierce attack on children’s health insurance, beset by politically inconvenient retirements and uncertain if another scandal lurks around the corner, Congressional Republicans are feeling a bit under siege as even one of their former leaders predicts 2008 could be a Democratic year.* * * The twist is that the issue Republicans had feared most in the fall, the war in Iraq, has played out legislatively in their favor for the moment. * * * But Republicans say they have lacked a similar cohesive plan to counter the Democratic assault over the children’s health insurance program that will be the subject of a veto override vote in the House on Thursday. President Bush’s veto of an expansion of that program and the strategic failure have exposed vulnerable Republicans to a backlash and allowed the party to be painted as uncaring.