against the wall

According to Howard there is much to fear about "wall-to-wall Labor governments":

"Such a state of affairs would rob this country of the necessary checks and balances that a federal system inevitably provides."

Well, surely it's not quite as dire as that. Voters are still able to vote Liberal at the next state elections. At worst it’s a short-term lack of balance, which presents little risk.
Making a big deal of this checks-and-balances argument means Howard puts himself in a position where, if the Liberals are in power federally, he must really argue against voting in a number of Liberal state governments. Anyway, if Labor were in government federally, maybe people would be more willing to give state Liberal parties a go? The onus is simply on the Liberals to come up with credible state alternatives. (When it was down to Iemma v Debnam, it was a no-brainer. But Iemma v O’Farrell? Different story...)
If we can’t vote a federal government out just because of what is occurring at state level, it makes it impossible to hold a federal government accountable on its own merits (or lack thereof).
And let’s not forget how, in recent times, Howard has been working hard at trying to absorb various state powers. As such, voting Liberal federally means accepting such further weakening of the powers of the state governments that you ostensibly voted in as checks-and-balances against federal power. Hmm...it’s a tangled web, innit?