Simple household arithmetic. Clinton increased income and cut expenses. Bush cut income and increased expenses. You know and I know that if your household income is $30,000 and your household expenses are $20,000, that other $10,000 can be used to lower your indebtedness--you can pay off your mortgage or your car faster. Or not--you can choose to save it, too. But at any rate, if your income is larger than your expenses you have that choice. If, on the other hand, you take a pay cut to $20,000 and increase your spending to $30,000, your indebtedness is going to shoot up.
Bush came into office with the express intent (and support of a "fiscally conservative" Congress) to cut taxes (thus cutting the federal government's income) and also to increase defense spending, which he felt had been under-supported. Now if you want to spend more, most people (including conservatives in government) will tell you, the individual, that you need to increase your income. Take that second or third job. But that's not what GOP (in the persons of Bush's Administration or Congress) did. After 9/11, there was suddenly an excuse to spend a lot more money on "national security"--something that certainly pleased certain corporations whose personnel, services, and products fell in that sector.
First, the creation of an entire new cabinet-level department, "Homeland Security" (rather than horsewhipping the existing agencies into cooperating as they'd been told before to do) that duplicated some functions, and created others, at great expense. Such as the infamous "Border Fence" (a million dollars a mile. And there are a lot of miles on the US/Mexican border.) Such as the "Patriot Act" and all its successors that led to such things as imprisonment without proper judicial procedures, "renditions," etc.
Second, Bush's determination to find an excuse to attack his "axis of evil". The runup to the war in Iraq was expensive (and profitable to those providing the stuff bought) and Bush's Administration was perfectly willing to accept any evidence for (and none against) the "weapons of mass destruction" argument for invading Iraq. Much of the expense was hidden from Congress (though the GOPs in Congress have never squealed about it the way they should have, party loyalty being paramount these days--compare that to the outrage of GOP Congresscritters when they found Nixon had lied to them.) It was kept out of the budget...but not out of the balance books.
Third, the cost of the war once it started. Wars are predictably expensive...known to be expensive...and predictably underfunded without a large increase in taxes. Bush and company did not increase income to meet this massive new expense even when they enlarged it by invading Afghanistan. Eliminating tax custs at the start of the war would have helped cover the cost (only helped--they'd have needed to raise taxes above the previous levels to actually pay for it in an ongoing way.) Instead, they continued to blame the rising national debt on those who weren't responsible.
Fourth, the Bush Administration and the GOP dominated Congress did not even enforce the fees that should have been paid by energy-industry corporations (for drilling permits in the Gulf of Mexico, for instance) that, though too small, might have offset some of the increased expenditures. Deregulation was the order of the day, and considerable money was owed was not collected.
Fifth, the Bush Administration and Congress agreed to bail out the financial sector with nearly five trillion dollars, at the end of Bush's presidency. Trillion. (Among corporations paying no, or minimal, income tax last year are three that were bailed out at the end of 2008: Bank of America, Goldman-Sachs, and Citibank, all of whom now report profits. ) Because some of that money was paid out in early 2009 (having been voted by Congress in 2008) many people blame the Obama Administration and a Democratic Congress for it--but that's not accurate.
In other words, the GOP in control of both the executive and legislative branches of the federal govenment spent money like water on whatever they wanted, while cutting income. If the GOP were a woman spending beyond her money on shoes, jewels, hairdressers, clothes, and if she decided to spend a huge amount treating her friends to a lavish bash just before skipping town, the moralists in that camp would be all over her for her greedy, self-indulgent, ostentatious splurging....but since it was they themselves doing the spending, and their friends who were being spent on (Halliburton's contracts in Iraq and post-Katrina, Blackwater, military contractors, oil & other energy companies) they always had the excuse of "national security." While at the same time, they could use the same excuse to tighten control of individual lives, intruding into what had been--and should be--an individual's right to privacy in (for instance) medical decisions, adult sexual practices, expressions of opinion, religious choices, and spoken and written communication with others. They were happy to treat most of us as potential if not actual criminals. But that's for another chapter.
When anyone in the GOP brings up the national debt, the question to ask is "Why did not the President and Congress increase income to cover the cost of the wars they chose to engage it? Why did not the President and Congress take responsibility for the financial sector bailout that put a huge new load on the national debt?"
Even GOP supporters know and will admit that when individuals shut off one source of income and then spend more, they're going to run out of money and be in debt. The GOP in general is very negative about individual debt (people should have more self discipline, they'll say smugly.) But the GOP is surprisingly tolerant of running up a government debt if it benefits the right parties (not, of course, individuals in need.)