Republican and Democratic orthodoxy
 
Orthodox Republicans accept  all or most of these positions
1. No income tax income increases  for the rich. 
2. Do not believe in human caused global warming, or simply do not want government trying to manage the problem.
3. Believe in only limited government regulation on businesses except when it helps your bottom line.
4. Believe in maintaining  a strong national defense-this one never changes!
5. No  public financing for elections, and only limited regulation of campaign contributions
6. Do not like unions.
7. Do not believe in universal health coverage
8. Pro-life (though it's OK to not do anything about it, other than appointing conservative judges) 
9. Not a fan of  academia or  of the mainstream news media.  
10.No  amnesty for illegal aliens, but don't be serious about  enough to   solve the problem by  actually deporting   all 11 million of them.
If   you can't check at least 9 of these 10 your a Rhino (   Republican-In-Name only).  As far as a I  know, Sarah Palin &   Michelle Bachmann  can check all of these. Rush Limbaugh and Sean  Hannity would both get  perfect scores as well.   Rick Perry can check 9  out of 10 (he fails on  immigration policy). George W. Bush would able  to check  9 of 10 as well. Mitt  Romney, has at various points not been  able to  check at least two of these, though Mitt is trying to lean in a  more   orthodox  direction on most of these items.  John McCain fails  this test on at  least two of the ten though  it's unclear as to what  his actual score should be.  
There are   a  few other points of orthodoxy (American Exceptional-ism.  Gun rights,  Enhanced Interrogation), but there begins   to be more free   thinking when you get beyond these first ten. Libertarians sometimes   clash with social conservatives. Less educated populist Republicans   clash with Wall street types. 
Foreign Policy is a special case.  While it's expected that Orthodox  Republicans will  disagree with  Obama's foreign policy, it's probably  true that some Republicans might  agree with aspects of Obama's foreign  policy if a Republican President  was carrying them out  (For example  some aspects of his   Libyan and Afghanistan polices). Republicans are  little less confident  than they used to be on Foreign Policy after the  Iraq War. Orthodox  Republicans still believe that the Iraq War was the  right thing to do ,  but recognize that they did lose some Independent  and  Blue Dog  Democrats votes in 2008 because of Bush's handling of  the  Iraq War. 
 At  the present time, orthodoxy  favors  business conservatives over  social conservatives which means that it's  OK to not be overly  concerned about  having prayer in school, or be too  worried about gay   marriage.  And there is some suspicion of Wall Street among some  in the   Tea Party, which isn't true of establishment Republicans. During the    George W. Bush years, there was an indifference  to balancing  budgets,  and a predilection for earmark spending, however  now orthodoxy is   moving more towards wanting to actually balance the Federal  budget as a   backdoor way of actually shrinking government.
Republicans have found  that orthodoxy works for them, because when they  walk in lock step they,  can keep their coalition together, seem more  principled, and have a  more energized base.  
What are the litmus tests for being a Democratic politician?
Generally you have to...
1. Favor some kind of attempt at universal health coverage 
2. Be pro-choice (it's OK to 
say your personally opposed to abortion).  
3. Be willing  to raise taxes on rich people, and be rather  indifferent   to that fact that the poor and lower middle class don't pay much  income  tax, though usually taxes of any kind are OK at the state level.
4. Like vigorous government regulation, sometimes even when it is anti-growth. 
5. Believe in  some form of leniency or amnesty for undocumented immigrants. A particular blind spot for liberals.. 
6. Support  unions, especially teacher unions.   
7. Agree that  humans cause at least some of the Global warming problem, though this one has gone to the back burner.
8.  Be OK with  government Stimulus spending, have an inordinate faith  in  Keynesian economics, and not recognize that businesses create most  jobs,  not government. 
Anybody  running for the President in the Democrat party would probably  be able  to check all these.   But there is diversity of  opinion-  liberals  would  prefer a single payer health plan.   Moderate   Democrats like     balanced  budgets, and establishment democrats are OK  with America's  role as the world's policemen, while Liberals want us  to stop fighting wars. Some Democrats support Israel, some  don't.  
Democrats have always had more problems with  staying in  lockstep,  because on the Presidential  level, voters don't usually vote  for  liberal candidates, but will vote for moderate  Democrats.  Obama  was  the exception to the rule, the first clearly liberal president since  at  least Lyndon Johnson.  It is hard to govern completely as a liberal   president in a relatively conservative nation , and Obama has sometimes   had to govern from the center, which angers his base, but has done   nothing for him with Republicans, or Independents.