my $string = "huckabee AND jfkadlsfj  fdsfldfj06329 OR reagan AND biden AND clinton OR sebelius OR mccain";

my @chunks = split / AND /, $string;
@chunks = map { /OR/ ? "($_)" : $_ } @chunks;
print join(' AND ', @chunks), "\n";
__END__
huckabee AND (jfkadlsfj  fdsfldfj06329 OR reagan) AND biden AND (clinton OR sebelius OR mccain)