I would not blame any individual GOP politician, so much as an attitude and worldview that gradually came into being and took root, starting way back in the era of the Nixon resignation, with a trajectory something like this:
• Nixon resigns in disgrace; Democrats joyfully opine that this could return the country to a long Democratic rule, and the Nixon era dismissed as an anomaly caused by conservative reaction to the turbulence of the 60s; Carter defeats Ford in '76.
• Reagan defeats Carter and his politics are distinctively conservative, he’s the first conservative (as opposed to moderate) Republican president in, like, forever, and he’s popular; his re-election is a landslide, echoing the Nixon landslide against McGovern, and now it is the Republicans who see the country returning to its roots and the Carter administration is dismissed as an anomaly caused by the country’s reaction to Watergate; Congress goes Republican for the first time in, like, forever. The religious right thinks in terms of Destiny with a capital D, and there’s a spirit among the conservatives that they’ve got a permanent lock on American politics, that liberalism is dead, etc; after Reagan, Bush defeats Dukakis.
• Clinton defeats Bush and the Republicans and their conservative constituency are apoplectic! Bloody hell, Carter was just an anomaly, right? THIS wasn’t supposed to happen! It’s another anomaly obviously, let’s block him and push his liberal ass offstage ASAP and get back to running the country. But Clinton beats Dole and is re-elected despite Monica Lewinsky and the impeachment proceedings. Republican voters and conservatives and the religious right becomes ever more insistent on ending this horrible cheating anomaly that is occupying the space that rightfully belongs to them, the ascendant new permanent conservative majority and so on and so forth.
• Bush II defeats Gore in the razor-close & controversial election of 2000. He campaigns as Conservative Lite (this fact is often forgotten when looking back); Democrats and liberals hate him less for anything he’s doing in office than for stealing the election (Gore won the popular vote, Bush the electoral college via winning Florida by a razor’s margin requiring recounts / conservative Supreme Ct judges and Florida officials were perceived as settling the issue on partisan grounds).
• Events of 911 cause nation to rally around the leader; 1 year later he changes course with invasion of Iraq and Democrats and liberals are outraged; he opts for more conservative domestic politics also; Democrats try to unseat him but he beats Kerry; during his second term Democrats and liberals treat him as an anomaly, unfairly in power and abusive of it, benefitting from 911 wartime patriotism, and they want him gone ASAP
• Obama beats McCain and Republicans continue to react as if the White House naturally belongs to them and any Democrat occupying it is an anomaly who must be blocked at every turn and shoved offstage. They obstruct as much as possible. Obama beats Romney and they remain furious and continue to obstruct as much as possible.
Note that both contingents have come to think of the other party’s occupation of the White House as anomalous and accidental; but the Republicans / conservatives have been especially prone to think that the American voters will NOT mind if they block and obstruct and use hardball tactics to interfere with the Democratic president’s administration, because they think the American voters agree with them that the place rightfully belongs to the Republicans and that the Democrats don’t belong there and should not by any rights be exercising any power there. The Democrats and liberals are less nutcase about it and believe they will prevail most of the time (the EC has become their turf) but are inclined to think that if they misbehave, voters will indeed hold them accountable.