In what ways do issues related to debt and poverty challenge the values of liberalism?

It doesn't because it's conservatives who have that problem!

Want to talk about how Trump and the Republicans raised the deficit since he took office?

Definition of "liberalism" as defined in "Lecture At Yale University": "By liberalism I don't mean the creed of any party or any century. I mean a generosity of spirit, a tolerance for others, an effort to comprehend otherness, a high ideal for the dignity and value of humanity, a commitment to the rule of law, a repugnance for authoritarianism, and a love of freedom."

The wise adage that best applies to your question: "A chain (or nation) can only be as strong as its weakest link." Those who seek to build and then maintain a strong nation make sure that all of our "links" are made stronger, sometimes with social safety nets, sometimes with new opportunities, unions to protect workers, and also with a strong economy---such as the FDR "New Deal" to get us out of the Republican-caused Great Depression; the BALANCED BUDGET of "West Wing" inspiration President Bill Clinton and his Democrat-controlled first Congress (1992-1994) that passed a revenues-generating, deficit-eliminating 39% fair-share tax rate for billionaires and the richest corporations (like Koch industries et al.), and the deficit-slashing miracles of the Obama/Biden administration and their high-powered 111th Democrat-controlled Congress (2009-2011), where liberal House Speaker Nancy Pelosi was able to get more than 362 quality pieces of legislation passed through to Senator Harry Reid and his Republican-controlled Senate---signed into law. Speaker Pelosi always insists on having her PAY-GO RULE in place when she takes the gavel, where every dollar spent for our national budget has to be offset by a dollar cut from elsewhere in that budget, to include having billionaires and the richest corporations pay a fair-share contribution in taxes.

Does this help you understand?

They don't really challenge actual or classical liberalism as much as debt and poverty are the RESULT of post-modern progressivism. The Marxist worldview is such that it sees equality of misery and poverty as superior to a surplus economy where even the poorest are taken care of, but where anyone is allowed to be richer than anyone else.

Your question is very broad. The debt problem we have had is directly traceable to Republican borrow and spend with tax cuts for billionaires. Add to that Republican hostility to birth control and Republicans are the root cause of our problems.

Trump socialist debt

HOW to SQUEEZE MORE TAXES out of a rock ....................

A lot.