National's debt reduction target is the least ambitious it could possibly be, says a leading economist.If it is returned to power after November's election, National will introduce three "budget responsibility rules": returning to surplus in 2028/29, reducing debt below 40 percent of GDP and lowering government spending towards 30 percent of GDP over time.Leader Christopher Luxon said if the government's books were not in order, the country was vulnerable to economic shocks.He criticised Labour during Sunday's announcement, blaming the former government for racking up debt as it tackled the Covid-19 pandemic, and eroding a buffer that was necessary for dealing with the next major shock.Infometrics chief economist Brad Olsen said National's focus on fiscal discipline was encouraging, but it was simply committing to continuing the coalition's current fiscal strategy."The focus from the National Party of trying to get debt ... down to below 40 percent is probably the least ambitious they could have possibly been," he said."Previously, we've heard the National Party talk a lot more about trying to get debt back to 20 percent of GDP, and so [it's a] step in the right direction and necessary step, but not nearly as far, or as, I guess, expansive of a policy or position that they could have taken, and have taken before."Olsen said the aim to lowering government spending to 30 percent of GDP was about right.Infometrics chief economist Brad OlsenRNZ / Samuel RillstoneHe questioned what National might cut, given it had effectively ruled out new taxes, limiting its revenue."That only leaves the ability to limit expenses and tone down government spending as the options available," he said.Olsen said New Zealand's debt was lower than a number of comparable countries, but it needed to be, given it was a small island nation with fewer taxpayers, was reliant on trading partners and carried a greater risk of natural disasters."We always want to have that lower level of debt capacity, so that we've got the space to respond to the next pandemic, the next natural disaster, whatever it might be."Spending to support the country through the pandemic worked initially, but it went on too long and had been difficult to unwind, Olsen said.Labour's finance spokesperson Barbara Edmonds said her party did what was necessary to buffer the economic shock.She said National's rules would simply continue the government's current fiscal strategy, which was failing New Zealanders.Edmonds pointed to unemployment reaching an 11-year high and a surge in the number of people making KiwiSaver withdrawals due to financial hardship.ACT Party leader David Seymour said National could only achieve its budget goals with his party's help.He claimed victory over cutting costs on a number of initiatives this term."Without ACT, the taxpayer would be on the hook for billions more, but even more savings are needed."To make these budget goals real will require ACT at the Cabinet table."